diff --git a/Software/PC_Application/LibreVNA-GUI/Device/virtualdevice.cpp b/Software/PC_Application/LibreVNA-GUI/Device/virtualdevice.cpp
index 8544a66..dad5535 100644
--- a/Software/PC_Application/LibreVNA-GUI/Device/virtualdevice.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Device/virtualdevice.cpp
@@ -110,7 +110,7 @@ VirtualDevice::VirtualDevice(QString serial)
     zerospan = false;
 
     // Check if this is a compound device
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     for(auto cd : pref.compoundDevices) {
         if(cd->name == serial) {
             // connect request to this compound device
@@ -257,8 +257,8 @@ bool VirtualDevice::setVNA(const VirtualDevice::VNASettings &s, std::function<vo
         portStageMapping[s.excitedPorts[i]] = i;
     }
 
-    auto pref = Preferences::getInstance();
-    Protocol::SweepSettings sd;
+    auto& pref = Preferences::getInstance();
+    Protocol::SweepSettings sd = {};
     sd.f_start = s.freqStart;
     sd.f_stop = s.freqStop;
     sd.points = s.points;
@@ -335,8 +335,8 @@ bool VirtualDevice::setSA(const VirtualDevice::SASettings &s, std::function<void
         return false;
     }
     zerospan = s.freqStart == s.freqStop;
-    auto pref = Preferences::getInstance();
-    Protocol::SpectrumAnalyzerSettings sd;
+    auto& pref = Preferences::getInstance();
+    Protocol::SpectrumAnalyzerSettings sd = {};
     sd.f_start = s.freqStart;
     sd.f_stop = s.freqStop;
     sd.pointNum = s.points;
@@ -410,8 +410,8 @@ bool VirtualDevice::setSG(const SGSettings &s)
     if(!info.supportsSGmode) {
         return false;
     }
-    auto pref = Preferences::getInstance();
-    Protocol::PacketInfo packet;
+    auto& pref = Preferences::getInstance();
+    Protocol::PacketInfo packet = {};
     packet.type = Protocol::PacketType::Generator;
     Protocol::GeneratorSettings &sd = packet.generator;
     sd.frequency = s.freq;
@@ -485,7 +485,7 @@ bool VirtualDevice::setExtRef(QString option_in, QString option_out)
         refOut = Reference::OutFreq::Off;
     }
 
-    Protocol::PacketInfo p;
+    Protocol::PacketInfo p = {};
     p.type = Protocol::PacketType::Reference;
     switch(refIn) {
     case Reference::TypeIn::Internal:
@@ -518,7 +518,7 @@ bool VirtualDevice::setExtRef(QString option_in, QString option_out)
 
 std::set<QString> VirtualDevice::GetAvailableVirtualDevices()
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     auto ret = Device::GetDevices();
     // Add compound devices as well
     for(auto vdev : pref.compoundDevices) {
diff --git a/Software/PC_Application/LibreVNA-GUI/Generator/generator.cpp b/Software/PC_Application/LibreVNA-GUI/Generator/generator.cpp
index 3b5b923..3cece8b 100644
--- a/Software/PC_Application/LibreVNA-GUI/Generator/generator.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Generator/generator.cpp
@@ -7,7 +7,7 @@ Generator::Generator(AppWindow *window, QString name)
 {
     central = new SignalgeneratorWidget(window, window);
 
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     // set initial values
     if(pref.Startup.RememberSweepSettings) {
diff --git a/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp b/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
index 513bf09..516a823 100644
--- a/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/SpectrumAnalyzer/spectrumanalyzer.cpp
@@ -264,7 +264,7 @@ SpectrumAnalyzer::SpectrumAnalyzer(AppWindow *window, QString name)
     SetTGEnabled(false);
 
     // Set initial sweep settings
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     if(pref.Acquisition.useMedianAveraging) {
         average.setMode(Averaging::Mode::Median);
@@ -1130,7 +1130,7 @@ void SpectrumAnalyzer::ConstrainAndUpdateFrequencies()
 void SpectrumAnalyzer::LoadSweepSettings()
 {
     QSettings s;
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     settings.freqStart = s.value("SAStart", pref.Startup.SA.start).toULongLong();
     settings.freqStop = s.value("SAStop", pref.Startup.SA.stop).toULongLong();
     ConstrainAndUpdateFrequencies();
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
index 0830a17..f1574a5 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
@@ -16,6 +16,7 @@
 #include <QActionGroup>
 #include <QApplication>
 #include <QDateTime>
+#include <QCheckBox>
 
 using namespace std;
 
@@ -24,6 +25,9 @@ Marker::Marker(MarkerModel *model, int number, Marker *parent, QString descr)
       model(model),
       parentTrace(nullptr),
       position(1000000000),
+      minPosition(0),
+      maxPosition(0),
+      restrictPosition(false),
       number(number),
       visible(true),
       data(0),
@@ -87,7 +91,7 @@ void Marker::assignTrace(Trace *t)
     if(firstAssignment) {
         // Marker was just created and this is the first assignment to a trace.
         // Use display format on graph from preferences
-        auto p = Preferences::getInstance();
+        auto& p = Preferences::getInstance();
         if(p.Marker.defaultBehavior.showDataOnGraphs) {
             if(p.Marker.defaultBehavior.showAllData) {
                 for(auto f : applicableFormats()) {
@@ -644,6 +648,22 @@ QString Marker::readableType()
     }
 }
 
+QString Marker::domainToUnit()
+{
+    return domainToUnit(getDomain());
+}
+
+QString Marker::domainToUnit(Trace::DataType domain)
+{
+    switch(domain) {
+    case Trace::DataType::Frequency: return "Hz";
+    case Trace::DataType::Power: return "dBm";
+    case Trace::DataType::Time: return "s";
+    case Trace::DataType::TimeZeroSpan: return "s";
+    }
+    return "";
+}
+
 void Marker::setPosition(double pos)
 {
     position = pos;
@@ -938,6 +958,14 @@ void Marker::constrainPosition()
 {
     if(parentTrace) {
         if(parentTrace->size() > 0)  {
+            if(restrictPosition) {
+                if(position > maxPosition) {
+                    position = maxPosition;
+                }
+                if(position < minPosition) {
+                    position = minPosition;
+                }
+            }
             if(position > parentTrace->maxX()) {
                 position = parentTrace->maxX();
             } else if(position < parentTrace->minX()) {
@@ -1166,6 +1194,9 @@ nlohmann::json Marker::toJSON()
     j["type"] = typeToString(type).toStdString();
     j["number"] = number;
     j["position"] = position;
+    j["minPosition"] = minPosition;
+    j["maxPosition"] = maxPosition;
+    j["restrictPosition"] = restrictPosition;
     if(group) {
         j["group"] = group->getNumber();
     }
@@ -1205,6 +1236,9 @@ void Marker::fromJSON(nlohmann::json j)
     creationTimestamp = j.value("creationTimestamp", QDateTime::currentSecsSinceEpoch());
     number = j.value("number", 1);
     position = j.value("position", 0.0);
+    minPosition = j.value("minPosition", 0.0);
+    maxPosition = j.value("maxPosition", 0.0);
+    restrictPosition = j.value("restrictPosition", false);
     visible = j.value("visible", true);
 
     unsigned int hash = j["trace"];
@@ -1458,6 +1492,59 @@ SIUnitEdit *Marker::getSettingsEditor()
     return ret;
 }
 
+QWidget *Marker::getRestrictEditor()
+{
+    auto w = new QWidget;
+    auto layout = new QHBoxLayout;
+    layout->setContentsMargins(0,0,0,0);
+    auto cb = new QCheckBox;
+    cb->setChecked(restrictPosition);
+    layout->addWidget(cb);
+    auto min = new SIUnitEdit;
+    min->setPrefixes("pnum kMG");
+    min->setUnit(domainToUnit());
+    min->setPrecision(5);
+    min->setValue(minPosition);
+    min->setEnabled(restrictPosition);
+    layout->addWidget(new QLabel("from"));
+    layout->addWidget(min);
+    auto max = new SIUnitEdit;
+    max->setPrefixes("pnum kMG");
+    max->setUnit(domainToUnit());
+    max->setPrecision(5);
+    max->setValue(maxPosition);
+    max->setEnabled(restrictPosition);
+    layout->addWidget(new QLabel("to"));
+    layout->addWidget(max);
+
+    connect(cb, &QCheckBox::toggled, this, [=](){
+        restrictPosition = cb->isChecked();
+        min->setEnabled(restrictPosition);
+        max->setEnabled(restrictPosition);
+        constrainPosition();
+        update();
+    });
+    connect(min, &SIUnitEdit::valueChanged, this, [=](){
+        minPosition = min->value();
+        if(maxPosition < minPosition) {
+            maxPosition = minPosition;
+            max->setValueQuiet(maxPosition);
+        }
+        constrainPosition();
+    });
+    connect(max, &SIUnitEdit::valueChanged, this, [=](){
+        maxPosition = max->value();
+        if(maxPosition < minPosition) {
+            minPosition = maxPosition;
+            min->setValueQuiet(minPosition);
+        }
+        constrainPosition();
+    });
+
+    w->setLayout(layout);
+    return w;
+}
+
 void Marker::adjustSettings(double value)
 {
     switch(getDomain()) {
@@ -1565,20 +1652,22 @@ void Marker::update()
         // empty trace, nothing to do
         return;
     }
+    auto xmin = restrictPosition ? minPosition : numeric_limits<double>::lowest();
+    auto xmax = restrictPosition ? maxPosition : numeric_limits<double>::max();
     switch(type) {
     case Type::Manual:
     case Type::Delta:
         // nothing to do
         break;
     case Type::Maximum:
-        setPosition(parentTrace->findExtremum(true));
+        setPosition(parentTrace->findExtremum(true, xmin, xmax));
         break;
     case Type::Minimum:
-        setPosition(parentTrace->findExtremum(false));
+        setPosition(parentTrace->findExtremum(false, xmin, xmax));
         break;
     case Type::PeakTable: {
         deleteHelperMarkers();
-        auto peaks = parentTrace->findPeakFrequencies(100, peakThreshold);
+        auto peaks = parentTrace->findPeakFrequencies(100, peakThreshold, 3.0, xmin, xmax);
         char suffix = 'a';
         for(auto p : peaks) {
             auto helper = new Marker(model, number, this);
@@ -1600,7 +1689,7 @@ void Marker::update()
             break;
         } else {
             // find the maximum
-            auto peakFreq = parentTrace->findExtremum(true);
+            auto peakFreq = parentTrace->findExtremum(true, xmin, xmax);
             // this marker shows the insertion loss
             setPosition(peakFreq);
             // find the cutoff frequency
@@ -1609,7 +1698,11 @@ void Marker::update()
             auto cutoff = peakAmplitude + cutoffAmplitude;
             int inc = type == Type::Lowpass ? 1 : -1;
             while(index >= 0 && index < (int) parentTrace->size()) {
-                auto amplitude = Util::SparamTodB(parentTrace->sample(index).y);
+                auto sample = parentTrace->sample(index);
+                if(sample.x > xmax) {
+                    break;
+                }
+                auto amplitude = Util::SparamTodB(sample.y);
                 if(amplitude <= cutoff) {
                     break;
                 }
@@ -1640,7 +1733,11 @@ void Marker::update()
 
             auto low_index = index;
             while(low_index >= 0) {
-                auto amplitude = Util::SparamTodB(parentTrace->sample(low_index).y);
+                auto sample = parentTrace->sample(low_index);
+                if(sample.x < xmin) {
+                    break;
+                }
+                auto amplitude = Util::SparamTodB(sample.y);
                 if(amplitude <= cutoff) {
                     break;
                 }
@@ -1654,7 +1751,11 @@ void Marker::update()
 
             auto high_index = index;
             while(high_index < (int) parentTrace->size()) {
-                auto amplitude = Util::SparamTodB(parentTrace->sample(high_index).y);
+                auto sample = parentTrace->sample(high_index);
+                if(sample.x > xmax) {
+                    break;
+                }
+                auto amplitude = Util::SparamTodB(sample.y);
                 if(amplitude <= cutoff) {
                     break;
                 }
@@ -1670,7 +1771,7 @@ void Marker::update()
         }
         break;
     case Type::TOI: {
-        auto peaks = parentTrace->findPeakFrequencies(2);
+        auto peaks = parentTrace->findPeakFrequencies(2, -100, 3.0, xmin, xmax);
         if(peaks.size() != 2) {
             // error finding peaks, do nothing
             break;
@@ -1691,13 +1792,16 @@ void Marker::update()
         break;
     case Type::P1dB: {
         // find maximum
-        auto maxpos = parentTrace->findExtremum(true);
+        auto maxpos = parentTrace->findExtremum(true, xmin, xmax);
         // starting at the maximum point, traverse trace data towards higher power levels until amplitude dropped by 1dB
         auto maxindex = parentTrace->index(maxpos);
         auto maxpower = abs(parentTrace->sample(maxindex).y);
-        double p1db = parentTrace->maxX();
+        double p1db = parentTrace->maxX() > xmax ? xmax : parentTrace->maxX();
         for(unsigned int i = maxindex; i < parentTrace->size(); i++) {
             auto sample = parentTrace->sample(i);
+            if(sample.x > xmax) {
+                break;
+            }
             if(Util::SparamTodB(maxpower) - Util::SparamTodB(sample.y) >= 1.0) {
                 p1db = sample.x;
                 break;
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
index 3aab71b..7a6ae17 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
@@ -15,7 +15,7 @@ class MarkerGroup;
 
 class Marker : public QObject, public Savable
 {
-    Q_OBJECT;
+    Q_OBJECT
 public:
     Marker(MarkerModel *model, int number = 1, Marker *parent = nullptr, QString descr = QString());
     ~Marker();
@@ -61,6 +61,8 @@ public:
     QString readableSettings();
     QString tooltipSettings();
     QString readableType();
+    QString domainToUnit();
+    static QString domainToUnit(Trace::DataType domain);
 
     double getPosition() const;
     std::complex<double> getData() const;
@@ -96,6 +98,7 @@ public:
     QWidget *getTypeEditor(QAbstractItemDelegate *delegate = nullptr);
     void updateTypeFromEditor(QWidget *c);
     SIUnitEdit* getSettingsEditor();
+    QWidget *getRestrictEditor();
     void adjustSettings(double value);
     bool isVisible();
     void setVisible(bool visible);
@@ -184,6 +187,9 @@ private:
     Trace *parentTrace;
     unsigned long creationTimestamp;
     double position;
+    double minPosition;
+    double maxPosition;
+    bool restrictPosition;
     int number;
     bool visible;
     // Frequency domain: S parameter
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
index 7fc38ea..b74a60f 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
@@ -279,6 +279,7 @@ QVariant MarkerModel::headerData(int section, Qt::Orientation orientation, int r
             case ColIndexTrace: return "Trace";
             case ColIndexType: return "Type";
             case ColIndexSettings: return "Settings";
+            case ColIndexRestrict: return "Restrict";
             case ColIndexData: return "Data";
             }
             break;
@@ -291,6 +292,7 @@ QVariant MarkerModel::headerData(int section, Qt::Orientation orientation, int r
             case ColIndexTrace: return "The trace from which the marker gets its data";
             case ColIndexType: return "Depending on marker type, it can be positioned by the user or will be set automatically";
             case ColIndexSettings: return "Configurable marker parameter, depends on the marker type";
+            case ColIndexRestrict: return "Restrict the range available for this marker";
             case ColIndexData: return "Tracedata at the marker position";
             }
             break;
@@ -334,6 +336,7 @@ Qt::ItemFlags MarkerModel::flags(const QModelIndex &index) const
     case ColIndexTrace: flags |= Qt::ItemIsEnabled | Qt::ItemIsEditable; break;
     case ColIndexType: flags |= Qt::ItemIsEnabled | Qt::ItemIsEditable; break;
     case ColIndexSettings: flags |= Qt::ItemIsEnabled | Qt::ItemIsEditable; break;
+    case ColIndexRestrict: flags |= Qt::ItemIsEnabled | Qt::ItemIsEditable; break;
     case ColIndexData: flags |= Qt::ItemIsEnabled; break;
     }
     auto marker = markerFromIndex(index);
@@ -524,3 +527,22 @@ void MarkerTypeDelegate::setModelData(QWidget *editor, QAbstractItemModel *, con
     auto marker = static_cast<const MarkerModel*>(index.model())->markerFromIndex(index);
     marker->updateTypeFromEditor(editor);
 }
+
+QSize MarkerRestrictDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const
+{
+    return QSize(0, rowHeight);
+}
+
+QWidget *MarkerRestrictDelegate::createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const
+{
+    auto marker = static_cast<const MarkerModel*>(index.model())->markerFromIndex(index);
+    auto editor = marker->getRestrictEditor();
+    editor->setMaximumHeight(rowHeight);
+    editor->setParent(parent);
+    return editor;
+}
+
+void MarkerRestrictDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const
+{
+    // nothing to do
+}
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.h b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.h
index 2fba1e3..f28677b 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.h
@@ -11,7 +11,7 @@
 
 class MarkerTraceDelegate : public QStyledItemDelegate
 {
-    Q_OBJECT;
+    Q_OBJECT
     QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const override;
     QWidget *createEditor(QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index) const override;
     void setEditorData(QWidget * editor, const QModelIndex & index) const override;
@@ -31,7 +31,7 @@ Q_DECLARE_METATYPE(MarkerWidgetTraceInfo)
 
 class MarkerTypeDelegate : public QStyledItemDelegate
 {
-    Q_OBJECT;
+    Q_OBJECT
     QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const override;
     QWidget *createEditor(QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index) const override;
     void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const override;
@@ -39,7 +39,15 @@ class MarkerTypeDelegate : public QStyledItemDelegate
 
 class MarkerSettingsDelegate : public QStyledItemDelegate
 {
-    Q_OBJECT;
+    Q_OBJECT
+    QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const override;
+    QWidget *createEditor(QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index) const override;
+    void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const override;
+};
+
+class MarkerRestrictDelegate : public QStyledItemDelegate
+{
+    Q_OBJECT
     QSize sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const override;
     QWidget *createEditor(QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index) const override;
     void setModelData(QWidget * editor, QAbstractItemModel * model, const QModelIndex & index) const override;
@@ -59,6 +67,7 @@ public:
         ColIndexTrace,
         ColIndexType,
         ColIndexSettings,
+        ColIndexRestrict,
         ColIndexData,
         ColIndexLast,
     };
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markerwidget.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markerwidget.cpp
index da6a187..4d53fa5 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markerwidget.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markerwidget.cpp
@@ -27,6 +27,7 @@ MarkerWidget::MarkerWidget(MarkerModel &model, QWidget *parent) :
     ui->treeView->setItemDelegateForColumn(MarkerModel::ColIndexTrace, new MarkerTraceDelegate);
     ui->treeView->setItemDelegateForColumn(MarkerModel::ColIndexType, new MarkerTypeDelegate);
     ui->treeView->setItemDelegateForColumn(MarkerModel::ColIndexSettings, new MarkerSettingsDelegate);
+    ui->treeView->setItemDelegateForColumn(MarkerModel::ColIndexRestrict, new MarkerRestrictDelegate);
 
     ui->treeView->setSelectionMode(QAbstractItemView::SelectionMode::ExtendedSelection);
     ui->treeView->installEventFilter(this);
@@ -36,6 +37,7 @@ MarkerWidget::MarkerWidget(MarkerModel &model, QWidget *parent) :
     ui->treeView->setColumnWidth(MarkerModel::ColIndexVisible, 20);
     ui->treeView->setColumnWidth(MarkerModel::ColIndexTrace, 60);
     ui->treeView->setColumnWidth(MarkerModel::ColIndexType, 120);
+    ui->treeView->setColumnWidth(MarkerModel::ColIndexRestrict, 200);
 
     ui->treeView->setContextMenuPolicy(Qt::CustomContextMenu);
     connect(ui->treeView, &QTreeView::customContextMenuRequested, [&](const QPoint &p){
@@ -175,7 +177,7 @@ bool MarkerWidget::eventFilter(QObject *, QEvent *event)
 void MarkerWidget::updatePersistentEditors()
 {
     for(int i=0;i<model.rowCount();i++) {
-        auto columns = {MarkerModel::ColIndexTrace, MarkerModel::ColIndexType};
+        auto columns = {MarkerModel::ColIndexTrace, MarkerModel::ColIndexType, MarkerModel::ColIndexRestrict};
         for(auto c : columns) {
             auto index = model.index(i, c);
             ui->treeView->closePersistentEditor(index);
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Math/timegate.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Math/timegate.cpp
index 6653daa..881aa75 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Math/timegate.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Math/timegate.cpp
@@ -334,7 +334,7 @@ void Math::TimeGateGraph::paintEvent(QPaintEvent *event)
     auto input = gate->getInput()->rData();
 
     Q_UNUSED(event)
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     QPainter p(this);
     // fill background
     p.setBackground(QBrush(pref.Graphs.Color.background));
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
index c3dd8b7..01ab6be 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/trace.cpp
@@ -1206,11 +1206,14 @@ double Trace::maxX()
     }
 }
 
-double Trace::findExtremum(bool max)
+double Trace::findExtremum(bool max, double xmin, double xmax)
 {
     double compare = max ? numeric_limits<double>::min() : numeric_limits<double>::max();
     double freq = 0.0;
     for(auto sample : lastMath->rData()) {
+        if(sample.x < xmin || sample.x > xmax) {
+            continue;
+        }
         double amplitude = abs(sample.y);
         if((max && (amplitude > compare)) || (!max && (amplitude < compare))) {
             // higher/lower extremum found
@@ -1221,7 +1224,7 @@ double Trace::findExtremum(bool max)
     return freq;
 }
 
-std::vector<double> Trace::findPeakFrequencies(unsigned int maxPeaks, double minLevel, double minValley)
+std::vector<double> Trace::findPeakFrequencies(unsigned int maxPeaks, double minLevel, double minValley, double xmin, double xmax)
 {
     if(lastMath->getDataType() != DataType::Frequency) {
         // not in frequency domain
@@ -1236,6 +1239,9 @@ std::vector<double> Trace::findPeakFrequencies(unsigned int maxPeaks, double min
     double max_dbm = -200.0;
     double min_dbm = 200.0;
     for(auto d : lastMath->rData()) {
+        if(d.x < xmin || d.x > xmax) {
+            continue;
+        }
         double dbm = Util::SparamTodB(d.y);
         if((dbm >= max_dbm) && (min_dbm <= dbm - minValley)) {
             // potential peak frequency
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/trace.h b/Software/PC_Application/LibreVNA-GUI/Traces/trace.h
index f66283b..0bc3ae4 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/trace.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/trace.h
@@ -67,13 +67,14 @@ public:
     unsigned int size() const;
     double minX();
     double maxX();
-    double findExtremum(bool max);
+    double findExtremum(bool max, double xmin = std::numeric_limits<double>::lowest(), double xmax = std::numeric_limits<double>::max());
     /* Searches for peaks in the trace data and returns the peak frequencies in ascending order.
      * Up to maxPeaks will be returned, with higher level peaks taking priority over lower level peaks.
      * Only peaks with at least minLevel will be considered.
      * To detect the next peak, the signal first has to drop at least minValley below the peak level.
      */
-    std::vector<double> findPeakFrequencies(unsigned int maxPeaks = 100, double minLevel = -100.0, double minValley = 3.0);
+    std::vector<double> findPeakFrequencies(unsigned int maxPeaks = 100, double minLevel = -100.0, double minValley = 3.0,
+                                            double xmin = std::numeric_limits<double>::lowest(), double xmax = std::numeric_limits<double>::max());
     enum class SampleType {
         Frequency,
         TimeImpulse,
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
index b11c46c..45c1d79 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
@@ -168,7 +168,7 @@ void TracePlot::paintEvent(QPaintEvent *event)
     }
 
     Q_UNUSED(event)
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     QPainter p(this);
 //    p.setRenderHint(QPainter::Antialiasing);
     // fill background
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/tracepolarchart.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/tracepolarchart.cpp
index df03e68..18da04c 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/tracepolarchart.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/tracepolarchart.cpp
@@ -80,7 +80,7 @@ void TracePolarChart::axisSetupDialog()
 }
 
 void TracePolarChart::draw(QPainter &p) {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     p.setRenderHint(QPainter::Antialiasing);
     auto w = p.window();
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/tracesmithchart.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/tracesmithchart.cpp
index 0922f75..4182952 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/tracesmithchart.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/tracesmithchart.cpp
@@ -189,7 +189,7 @@ bool TraceSmithChart::configureForTrace(Trace *t)
 }
 
 void TraceSmithChart::draw(QPainter &p) {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     // translate coordinate system so that the smith chart sits in the origin and has a size of 1
     auto w = p.window();
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/tracewaterfall.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/tracewaterfall.cpp
index 0a87df2..686be71 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/tracewaterfall.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/tracewaterfall.cpp
@@ -210,7 +210,7 @@ void TraceWaterfall::updateContextMenu()
 
 void TraceWaterfall::draw(QPainter &p)
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     int xAxisSpace = pref.Graphs.fontSizeAxis * 3;
     constexpr int topMargin = 10;
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/tracexyplot.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/tracexyplot.cpp
index b73882c..3556a1c 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/tracexyplot.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/tracexyplot.cpp
@@ -348,7 +348,7 @@ bool TraceXYPlot::supported(Trace *t)
 
 void TraceXYPlot::draw(QPainter &p)
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     limitPassing = true;
 
diff --git a/Software/PC_Application/LibreVNA-GUI/VNA/Deembedding/matchingnetwork.cpp b/Software/PC_Application/LibreVNA-GUI/VNA/Deembedding/matchingnetwork.cpp
index 35887aa..853a043 100644
--- a/Software/PC_Application/LibreVNA-GUI/VNA/Deembedding/matchingnetwork.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/VNA/Deembedding/matchingnetwork.cpp
@@ -61,8 +61,8 @@ void MatchingNetwork::transformDatapoint(VirtualDevice::VNAMeasurement &p)
         p.measurements[name] = corrected.m11;
     }
     // handle the rest of the measurements
-    for(int i=0;i<VirtualDevice::getInfo(VirtualDevice::getConnected()).ports;i++) {
-        for(int j=i+1;j<VirtualDevice::getInfo(VirtualDevice::getConnected()).ports;j++) {
+    for(int i=1;i<=VirtualDevice::getInfo(VirtualDevice::getConnected()).ports;i++) {
+        for(int j=i+1;j<=VirtualDevice::getInfo(VirtualDevice::getConnected()).ports;j++) {
             if(i == port) {
                 auto S = uncorrected.toSparam(i, j);
                 auto corrected = Sparam(m.p * ABCDparam(S, p.Z0), p.Z0);
diff --git a/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp b/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
index fab3262..0644674 100644
--- a/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/VNA/vna.cpp
@@ -80,7 +80,6 @@ VNA::VNA(AppWindow *window, QString name)
     auto calLoad = calMenu->addAction("Load");
     saveCal = calMenu->addAction("Save");
     calMenu->addSeparator();
-//    saveCal->setEnabled(false);
 
     connect(calLoad, &QAction::triggered, [=](){
         LoadCalibration("");
@@ -97,17 +96,15 @@ VNA::VNA(AppWindow *window, QString name)
     auto calData = calMenu->addAction("Calibration Measurements");
     connect(calData, &QAction::triggered, [=](){
         cal.edit();
-//       StartCalibrationDialog();
     });
 
     auto calEditKit = calMenu->addAction("Edit Calibration Kit");
     connect(calEditKit, &QAction::triggered, [=](){
-        cal.getKit().edit();
-//        cal.getCalibrationKit().edit([=](){
-//            if(calValid) {
-//                ApplyCalibration(cal.getType());
-//            }
-//        });
+        cal.getKit().edit([=](){
+            if(cal.getCaltype().type != Calibration::Type::None) {
+                cal.compute(cal.getCaltype());
+            }
+        });
     });
 
     auto calElectronic = calMenu->addAction("Electronic Calibration");
@@ -518,7 +515,7 @@ VNA::VNA(AppWindow *window, QString name)
     SetupSCPI();
 
     // Set initial sweep settings
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
 
     if(pref.Acquisition.useMedianAveraging) {
         average.setMode(Averaging::Mode::Median);
@@ -1408,7 +1405,7 @@ void VNA::SetupSCPI()
 
 void VNA::ConstrainAndUpdateFrequencies()
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     double maxFreq;
     if(pref.Acquisition.harmonicMixing) {
         maxFreq = VirtualDevice::getInfo(window->getDevice()).Limits.maxFreqHarmonic;
@@ -1435,7 +1432,7 @@ void VNA::ConstrainAndUpdateFrequencies()
 
 void VNA::LoadSweepSettings()
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     QSettings s;
     // frequency sweep settings
     settings.Freq.start = s.value("SweepFreqStart", pref.Startup.DefaultSweep.f_start).toULongLong();
diff --git a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
index d001a98..11f6618 100644
--- a/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/appwindow.cpp
@@ -171,7 +171,7 @@ AppWindow::AppWindow(QWidget *parent)
 
     SetupSCPI();
 
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     if(pref.Startup.UseSetupFile) {
         LoadSetup(pref.Startup.SetupFile);
     }
@@ -297,7 +297,7 @@ void AppWindow::SetupMenu()
 
 void AppWindow::closeEvent(QCloseEvent *event)
 {
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     if(pref.Startup.UseSetupFile && pref.Startup.AutosaveSetupFile) {
         SaveSetup(pref.Startup.SetupFile);
     }
@@ -983,7 +983,7 @@ void AppWindow::UpdateAcquisitionFrequencies()
     }
     Protocol::PacketInfo p;
     p.type = Protocol::PacketType::AcquisitionFrequencySettings;
-    auto pref = Preferences::getInstance();
+    auto& pref = Preferences::getInstance();
     p.acquisitionFrequencySettings.IF1 = pref.Acquisition.IF1;
     p.acquisitionFrequencySettings.ADCprescaler = pref.Acquisition.ADCprescaler;
     p.acquisitionFrequencySettings.DFTphaseInc = pref.Acquisition.DFTPhaseInc;
diff --git a/Software/PC_Application/LibreVNA-GUI/averaging.cpp b/Software/PC_Application/LibreVNA-GUI/averaging.cpp
index 84a32db..6b341db 100644
--- a/Software/PC_Application/LibreVNA-GUI/averaging.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/averaging.cpp
@@ -5,6 +5,7 @@ using namespace std;
 Averaging::Averaging()
 {
     averages = 1;
+    numMeasurements = 0;
     mode = Mode::Mean;
 }
 
diff --git a/Software/PC_Application/LibreVNA-GUI/averaging.h b/Software/PC_Application/LibreVNA-GUI/averaging.h
index 3f2d39e..a08c486 100644
--- a/Software/PC_Application/LibreVNA-GUI/averaging.h
+++ b/Software/PC_Application/LibreVNA-GUI/averaging.h
@@ -33,7 +33,6 @@ private:
     void process(unsigned int pointNum, std::vector<std::complex<double> > &data);
 
     std::vector<std::deque<std::vector<std::complex<double>>>> avg;
-    int maxPoints;
     unsigned int numMeasurements;
     unsigned int averages;
     Mode mode;
diff --git a/Software/PC_Application/LibreVNA-GUI/main.cpp b/Software/PC_Application/LibreVNA-GUI/main.cpp
index 33393a6..5b24c01 100644
--- a/Software/PC_Application/LibreVNA-GUI/main.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/main.cpp
@@ -20,6 +20,9 @@ int main(int argc, char *argv[]) {
 
     qSetMessagePattern("%{time process}: [%{type}] %{message}");
 
+    Device::RegisterTypes();
+    VirtualDevice::RegisterTypes();
+
     app = new QApplication(argc, argv);
     QCoreApplication::setOrganizationName("LibreVNA");
     QCoreApplication::setApplicationName("LibreVNA-GUI");
@@ -27,9 +30,6 @@ int main(int argc, char *argv[]) {
     QCoreApplication::setApplicationVersion(window->getAppVersion() + "-" +
                                             window->getAppGitHash().left(9));
 
-    Device::RegisterTypes();
-    VirtualDevice::RegisterTypes();
-
 #ifdef Q_OS_UNIX
     signal(SIGINT, tryExitGracefully);
 #endif
diff --git a/Software/PC_Application/LibreVNA-GUI/preferences.cpp b/Software/PC_Application/LibreVNA-GUI/preferences.cpp
index aa95f8e..67387a1 100644
--- a/Software/PC_Application/LibreVNA-GUI/preferences.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/preferences.cpp
@@ -389,6 +389,13 @@ void PreferencesDialog::updateFromGUI()
     p->nonTrivialWriting();
 }
 
+Preferences::~Preferences()
+{
+    for(auto cd : compoundDevices) {
+        delete cd;
+    }
+}
+
 void Preferences::load()
 {
     QSettings settings;
diff --git a/Software/PC_Application/LibreVNA-GUI/preferences.h b/Software/PC_Application/LibreVNA-GUI/preferences.h
index fab2a8e..00876c9 100644
--- a/Software/PC_Application/LibreVNA-GUI/preferences.h
+++ b/Software/PC_Application/LibreVNA-GUI/preferences.h
@@ -48,6 +48,8 @@ public:
     static Preferences& getInstance() {
         return instance;
     }
+    Preferences(const Preferences&) = delete;
+    ~Preferences();
     void load();
     void store();
     void edit();