diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
index c0207d4..60d854d 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.cpp
@@ -136,6 +136,9 @@ QString Marker::formatToString(Marker::Format f)
     case Format::CenterBandwidth: return "Center + Bandwidth";
     case Format::InsertionLoss: return "Insertion loss";
     case Format::P1dB: return "P1dB";
+    case Format::NonUniformity: return "Non-uniformity";
+    case Format::maxDeltaNeg: return "Max. Delta Negative";
+    case Format::maxDeltaPos: return "Max. Delta Positive";
     case Format::Last: return "";
     }
     return "";
@@ -262,6 +265,11 @@ std::vector<Marker::Format> Marker::applicableFormats()
             ret.push_back(Format::AvgTone);
             ret.push_back(Format::AvgModulationProduct);
             break;
+        case Type::NonUniformity:
+            ret.push_back(Format::NonUniformity);
+            ret.push_back(Format::maxDeltaNeg);
+            ret.push_back(Format::maxDeltaPos);
+            break;
         default:
             break;
         }
@@ -363,6 +371,15 @@ std::vector<Marker::Format> Marker::defaultActiveFormats()
     if(pref.Marker.defaultBehavior.showP1dB) {
         ret.push_back(Format::P1dB);
     }
+    if(pref.Marker.defaultBehavior.showNonUniformity) {
+        ret.push_back(Format::NonUniformity);
+    }
+    if(pref.Marker.defaultBehavior.showMaxDeltaNeg) {
+        ret.push_back(Format::maxDeltaNeg);
+    }
+    if(pref.Marker.defaultBehavior.showMaxDeltaPos) {
+        ret.push_back(Format::maxDeltaPos);
+    }
     return ret;
 }
 
@@ -549,6 +566,16 @@ QString Marker::readableData(Format f)
                 } else {
                     return "Input P1dB:"+Unit::ToString(position, "dBm", " ", 4);
                 }
+                break;
+            case Format::NonUniformity:
+                return "Non-uniformity:"+Unit::ToString(maxDeltaNeg+maxDeltaPos, "dB", " ", 4);
+                break;
+            case Format::maxDeltaNeg:
+                return "max. Δ-:"+Unit::ToString(maxDeltaNeg, "dB", " ", 4);
+                break;
+            case Format::maxDeltaPos:
+                return "max. Δ+:"+Unit::ToString(maxDeltaPos, "dB", " ", 4);
+                break;
             case Format::Last:
                 return "Invalid";
             }
@@ -625,6 +652,8 @@ QString Marker::readableSettings()
             return "none";
         case Type::PhaseNoise:
             return Unit::ToString(offset, "Hz", " kM", 4);
+        case Type::NonUniformity:
+            return "None";
         default:
             break;
         }
@@ -987,6 +1016,7 @@ std::set<Marker::Type> Marker::getSupportedTypes()
             supported.insert(Type::Minimum);
             supported.insert(Type::Delta);
             supported.insert(Type::PeakTable);
+            supported.insert(Type::NonUniformity);
             if(!parentTrace->isReflection()) {
                 supported.insert(Type::Lowpass);
                 supported.insert(Type::Highpass);
@@ -1172,6 +1202,9 @@ void Marker::setType(Marker::Type t)
     case Type::PhaseNoise:
         required_helpers = {{"o", "Offset", Type::Manual}};
         break;
+    case Type::NonUniformity:
+        required_helpers = {{"l", "Lower Limit", Type::Manual}, {"u", "Upper Limit", Type::Manual}};
+        break;
     default:
         break;
     }
@@ -1183,6 +1216,14 @@ void Marker::setType(Marker::Type t)
         helper->setType(h.type);
         helperMarkers.push_back(helper);
     }
+    if(type == Type::NonUniformity) {
+        // need to update when any of the helper markers is moved
+        for(auto h : helperMarkers) {
+            connect(h, &Marker::positionChanged, [=](){
+                setPosition((helperMarkers[0]->position + helperMarkers[1]->position)/2);
+            });
+        }
+    }
     constrainFormat();
 
     updateSymbol();
@@ -1881,6 +1922,32 @@ void Marker::update()
         setPosition(p1db);
     }
         break;
+    case Type::NonUniformity: {
+        auto dbLower = Util::SparamTodB(helperMarkers[0]->getData());
+        auto dbUpper = Util::SparamTodB(helperMarkers[1]->getData());
+        auto posLower = helperMarkers[0]->getPosition();
+        auto posUpper = helperMarkers[1]->getPosition();
+        if(posLower > posUpper) {
+            swap(posLower, posUpper);
+            swap(dbLower, dbUpper);
+        }
+        auto startIndex = parentTrace->index(posLower);
+        auto stopIndex = parentTrace->index(posUpper);
+        maxDeltaNeg = std::numeric_limits<double>::lowest();
+        maxDeltaPos = std::numeric_limits<double>::lowest();
+        for(int i=startIndex;i<=stopIndex;i++) {
+            auto dbTrace = Util::SparamTodB(parentTrace->sample(i).y);
+            auto dbStraightLine = Util::Scale((double) i, (double) startIndex, (double) stopIndex, dbLower, dbUpper);
+            auto delta = dbTrace - dbStraightLine;
+            if(delta > maxDeltaPos) {
+                maxDeltaPos = delta;
+            }
+            if(-delta > maxDeltaNeg) {
+                maxDeltaNeg = -delta;
+            }
+        }
+    }
+        break;
     case Type::Last:
         break;
     }
@@ -1905,6 +1972,10 @@ std::complex<double> Marker::getData() const
 bool Marker::isMovable()
 {
     if(parent) {
+        if(parent->type == Type::NonUniformity) {
+            // non-uniformity is the exception, it has movable helper markers
+            return true;
+        }
         // helper traces are never movable by the user
         return false;
     }
@@ -1920,6 +1991,19 @@ bool Marker::isMovable()
     }
 }
 
+bool Marker::isEditable()
+{
+    if(parent) {
+        if(parent->type == Type::NonUniformity) {
+            // non-uniformity is the exception, it has movable helper markers
+            return true;
+        }
+        // helper traces are never movable by the user
+        return false;
+    }
+    return true;
+}
+
 QPixmap &Marker::getSymbol()
 {
     return symbol;
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
index 3212698..203c319 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/marker.h
@@ -47,6 +47,9 @@ public:
         AvgModulationProduct,   // average level of modulation products
         // compression parameters
         P1dB,                   // power level at 1dB compression
+        NonUniformity,
+        maxDeltaPos,
+        maxDeltaNeg,
         // keep last at end
         Last,
     };
@@ -68,6 +71,7 @@ public:
     double getPosition() const;
     std::complex<double> getData() const;
     bool isMovable();
+    bool isEditable();
     Trace::DataType getDomain();
 
     QPixmap& getSymbol();
@@ -92,6 +96,7 @@ public:
         TOI,
         PhaseNoise,
         P1dB,
+        NonUniformity,
         // keep last at end
         Last,
     };
@@ -171,6 +176,7 @@ private:
         case Type::TOI: return "TOI/IP3";
         case Type::PhaseNoise: return "Phase noise";
         case Type::P1dB: return "1dB compression";
+        case Type::NonUniformity: return "Non-uniformity";
         default: return QString();
         }
     }
@@ -211,6 +217,10 @@ private:
     double peakThreshold;
     double offset;
 
+    // non-uniformity
+    double maxDeltaNeg;
+    double maxDeltaPos;
+
     Format formatTable;
     std::set<Format> formatGraph;
 
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
index 5ccc6c1..c089506 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Marker/markermodel.cpp
@@ -303,7 +303,7 @@ QVariant MarkerModel::headerData(int section, Qt::Orientation orientation, int r
 
 bool MarkerModel::setData(const QModelIndex &index, const QVariant &value, int)
 {
-    if((unsigned int) index.row() >= markers.size()) {
+    if(!index.isValid()) {
         return false;
     }
     auto m = markerFromIndex(index);
@@ -340,7 +340,7 @@ Qt::ItemFlags MarkerModel::flags(const QModelIndex &index) const
     case ColIndexData: flags |= Qt::ItemIsEnabled; break;
     }
     auto marker = markerFromIndex(index);
-    if(marker->getParent()) {
+    if(!marker->isEditable()) {
         // this is a helper marker -> nothing is editable
         flags &= ~Qt::ItemIsEditable;
     }
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
index 6baf18e..ac89e3f 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/traceplot.cpp
@@ -433,7 +433,7 @@ Marker *TracePlot::markerAtPosition(QPoint p, bool onlyMovable)
             continue;
         }
         auto markers = t.first->getMarkers();
-        for(auto m : markers) {
+        for(Marker* m : markers) {
             if(!m->isMovable() && onlyMovable) {
                 continue;
             }
@@ -448,6 +448,9 @@ Marker *TracePlot::markerAtPosition(QPoint p, bool onlyMovable)
                 closestDistance = distance;
                 if(m->getParent()) {
                     closestMarker = m->getParent();
+                    if(closestMarker->getType() == Marker::Type::NonUniformity) {
+                        closestMarker = m;
+                    }
                 } else {
                     closestMarker = m;
                 }
diff --git a/Software/PC_Application/LibreVNA-GUI/preferences.cpp b/Software/PC_Application/LibreVNA-GUI/preferences.cpp
index 1ce12b6..7b8ecf5 100644
--- a/Software/PC_Application/LibreVNA-GUI/preferences.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/preferences.cpp
@@ -380,6 +380,9 @@ void PreferencesDialog::setInitialGUIState()
     ui->MarkerShowAvgTone->setChecked(p->Marker.defaultBehavior.showAvgTone);
     ui->MarkerShowAvgMod->setChecked(p->Marker.defaultBehavior.showAvgModulation);
     ui->MarkerShowP1dB->setChecked(p->Marker.defaultBehavior.showP1dB);
+    ui->MarkerShowNonUniformity->setChecked(p->Marker.defaultBehavior.showNonUniformity);
+    ui->MarkerShowMaxDeltaNeg->setChecked(p->Marker.defaultBehavior.showMaxDeltaNeg);
+    ui->MarkerShowMaxDeltaPos->setChecked(p->Marker.defaultBehavior.showMaxDeltaPos);
     ui->MarkerInterpolate->setCurrentIndex(p->Marker.interpolatePoints ? 1 : 0);
     ui->MarkerSortOrder->setCurrentIndex((int) p->Marker.sortOrder);
     ui->MarkerSymbolStyle->setCurrentIndex((int) p->Marker.symbolStyle);
@@ -485,6 +488,9 @@ void PreferencesDialog::updateFromGUI()
     p->Marker.defaultBehavior.showAvgTone = ui->MarkerShowAvgTone->isChecked();
     p->Marker.defaultBehavior.showAvgModulation = ui->MarkerShowAvgMod->isChecked();
     p->Marker.defaultBehavior.showP1dB = ui->MarkerShowP1dB->isChecked();
+    p->Marker.defaultBehavior.showNonUniformity = ui->MarkerShowNonUniformity->isChecked();
+    p->Marker.defaultBehavior.showMaxDeltaNeg = ui->MarkerShowMaxDeltaNeg->isChecked();
+    p->Marker.defaultBehavior.showMaxDeltaPos = ui->MarkerShowMaxDeltaPos->isChecked();
     p->Marker.interpolatePoints = ui->MarkerInterpolate->currentIndex() == 1;
     p->Marker.sortOrder = (MarkerSortOrder) ui->MarkerSortOrder->currentIndex();
     p->Marker.symbolStyle = (MarkerSymbolStyle) ui->MarkerSymbolStyle->currentIndex();
diff --git a/Software/PC_Application/LibreVNA-GUI/preferences.h b/Software/PC_Application/LibreVNA-GUI/preferences.h
index 331ccf6..411b490 100644
--- a/Software/PC_Application/LibreVNA-GUI/preferences.h
+++ b/Software/PC_Application/LibreVNA-GUI/preferences.h
@@ -150,7 +150,7 @@ public:
         struct {
             bool showDataOnGraphs;
             bool showdB, showdBm, showdBuV, showdBAngle, showRealImag, showImpedance, showVSWR, showResistance, showCapacitance, showInductance, showQualityFactor;
-            bool showNoise, showPhasenoise, showCenterBandwidth, showCutoff, showInsertionLoss, showTOI, showAvgTone, showAvgModulation, showP1dB;
+            bool showNoise, showPhasenoise, showCenterBandwidth, showCutoff, showInsertionLoss, showTOI, showAvgTone, showAvgModulation, showP1dB, showNonUniformity, showMaxDeltaNeg, showMaxDeltaPos;
         } defaultBehavior;
         bool interpolatePoints;
         MarkerSortOrder sortOrder;
@@ -264,6 +264,9 @@ private:
         {&Marker.defaultBehavior.showAvgTone, "Marker.defaultBehavior.showAvgTone", true},
         {&Marker.defaultBehavior.showAvgModulation, "Marker.defaultBehavior.showAvgModulation", true},
         {&Marker.defaultBehavior.showP1dB, "Marker.defaultBehavior.showP1dB", true},
+        {&Marker.defaultBehavior.showNonUniformity, "Marker.defaultBehavior.showNonUniformity", true},
+        {&Marker.defaultBehavior.showMaxDeltaNeg, "Marker.defaultBehavior.showMaxDeltaNeg", true},
+        {&Marker.defaultBehavior.showMaxDeltaPos, "Marker.defaultBehavior.showMaxDeltaPos", true},
         {&Marker.interpolatePoints, "Marker.interpolatePoints", false},
         {&Marker.sortOrder, "Marker.sortOrder", MarkerSortOrder::PrefMarkerSortXCoord},
         {&Marker.symbolStyle, "Marker.symbolStyle", MarkerSymbolStyle::EmptyNumberAbove},
diff --git a/Software/PC_Application/LibreVNA-GUI/preferencesdialog.ui b/Software/PC_Application/LibreVNA-GUI/preferencesdialog.ui
index 5cfd6c7..6ea3bc0 100644
--- a/Software/PC_Application/LibreVNA-GUI/preferencesdialog.ui
+++ b/Software/PC_Application/LibreVNA-GUI/preferencesdialog.ui
@@ -93,7 +93,7 @@
         </size>
        </property>
        <property name="currentIndex">
-        <number>6</number>
+        <number>3</number>
        </property>
        <widget class="QWidget" name="Startup">
         <layout class="QHBoxLayout" name="horizontalLayout_4">
@@ -1457,7 +1457,7 @@
               <x>0</x>
               <y>0</y>
               <width>749</width>
-              <height>576</height>
+              <height>605</height>
              </rect>
             </property>
             <layout class="QVBoxLayout" name="verticalLayout_23">
@@ -1640,6 +1640,27 @@
                          </property>
                         </widget>
                        </item>
+                       <item>
+                        <widget class="QCheckBox" name="MarkerShowNonUniformity">
+                         <property name="text">
+                          <string>Non-uniformity</string>
+                         </property>
+                        </widget>
+                       </item>
+                       <item>
+                        <widget class="QCheckBox" name="MarkerShowMaxDeltaNeg">
+                         <property name="text">
+                          <string>Max. Delta Negative</string>
+                         </property>
+                        </widget>
+                       </item>
+                       <item>
+                        <widget class="QCheckBox" name="MarkerShowMaxDeltaPos">
+                         <property name="text">
+                          <string>Max. Delta Positive</string>
+                         </property>
+                        </widget>
+                       </item>
                       </layout>
                      </widget>
                     </item>
@@ -1774,8 +1795,8 @@
              <rect>
               <x>0</x>
               <y>0</y>
-              <width>763</width>
-              <height>561</height>
+              <width>168</width>
+              <height>127</height>
              </rect>
             </property>
             <layout class="QHBoxLayout" name="horizontalLayout_12">