diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/calibration.cpp b/Software/PC_Application/LibreVNA-GUI/Calibration/calibration.cpp
index 8711379..dcdf9c4 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/calibration.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/calibration.cpp
@@ -1469,6 +1469,9 @@ bool Calibration::canCompute(Calibration::CalType type, double *startFreq, doubl
             if(!meas) {
                 // missing measurement
                 return false;
+            } else if (!meas->readyForCalculation()){
+                // measurement not ready (either not calkit standard definded or no measurements
+                return false;
             } else {
                 foundMeasurements.push_back(meas);
             }
diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
index 564dc67..5520f7b 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.cpp
@@ -45,6 +45,9 @@ bool CalibrationMeasurement::Base::setStandard(CalStandard::Virtual *standard)
         if(supportedStandardTypes().count(standard->getType())) {
             // can use this standard
             this->standard = standard;
+            connect(standard, &CalStandard::Virtual::deleted, this, [=](){
+                setStandard(nullptr);
+            });
             emit standardChanged(standard);
             return true;
         } else {
@@ -53,6 +56,9 @@ bool CalibrationMeasurement::Base::setStandard(CalStandard::Virtual *standard)
         }
     } else {
         // nullptr passed, remove currently used standard
+        if(this->standard) {
+            disconnect(this->standard, &CalStandard::Virtual::deleted, this, nullptr);
+        }
         this->standard = nullptr;
         emit standardChanged(nullptr);
         return true;
@@ -117,6 +123,10 @@ QWidget *CalibrationMeasurement::Base::createStandardWidget()
             cbStandard->setCurrentText(s->getDescription());
         }
     }
+    if(standard == 0 && cbStandard->count() > 0) {
+        // no standard was selected but no there is one available
+        setStandard((CalStandard::Virtual*) cbStandard->itemData(0, Qt::UserRole).value<void*>());
+    }
 
     connect(cbStandard, qOverload<int>(&QComboBox::currentIndexChanged), [=](){
         auto s = (CalStandard::Virtual*) cbStandard->itemData(cbStandard->currentIndex(), Qt::UserRole).value<void*>();
diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.h b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.h
index 0458083..639012a 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.h
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/calibrationmeasurement.h
@@ -38,6 +38,7 @@ public:
     virtual double minFreq() = 0;
     virtual double maxFreq() = 0;
     virtual unsigned int numPoints() = 0;
+    virtual bool readyForCalculation() {return false;}
 
     static std::vector<Type> availableTypes();
     static QString TypeToString(Type type);
@@ -79,9 +80,10 @@ public:
     virtual double minFreq() override;
     virtual double maxFreq() override;
     virtual unsigned int numPoints() override {return points.size();}
+    virtual bool readyForCalculation() override {return standard && points.size() > 0;}
 
-    virtual void clearPoints();
-    virtual void addPoint(const VirtualDevice::VNAMeasurement &m);
+    virtual void clearPoints() override;
+    virtual void addPoint(const VirtualDevice::VNAMeasurement &m) override;
 
     virtual QWidget* createSettingsWidget() override;
 
@@ -179,9 +181,10 @@ public:
     virtual double minFreq() override;
     virtual double maxFreq() override;
     virtual unsigned int numPoints() override {return points.size();}
+    virtual bool readyForCalculation() override {return standard && points.size() > 0;}
 
-    virtual void clearPoints();
-    virtual void addPoint(const VirtualDevice::VNAMeasurement &m);
+    virtual void clearPoints() override;
+    virtual void addPoint(const VirtualDevice::VNAMeasurement &m) override;
 
     virtual QWidget* createSettingsWidget() override;
 
@@ -236,9 +239,10 @@ public:
     virtual double minFreq() override;
     virtual double maxFreq() override;
     virtual unsigned int numPoints() override;
+    virtual bool readyForCalculation() override {return points.size() > 0;}
 
-    virtual void clearPoints();
-    virtual void addPoint(const VirtualDevice::VNAMeasurement &m);
+    virtual void clearPoints() override;
+    virtual void addPoint(const VirtualDevice::VNAMeasurement &m) override;
 
     virtual QWidget* createStandardWidget() override;
     virtual QWidget* createSettingsWidget() override;
diff --git a/Software/PC_Application/LibreVNA-GUI/Calibration/calstandard.h b/Software/PC_Application/LibreVNA-GUI/Calibration/calstandard.h
index 3403ad2..460e763 100644
--- a/Software/PC_Application/LibreVNA-GUI/Calibration/calstandard.h
+++ b/Software/PC_Application/LibreVNA-GUI/Calibration/calstandard.h
@@ -11,11 +11,12 @@
 namespace CalStandard
 {
 
-class Virtual : public Savable
+class Virtual : public QObject, public Savable
 {
+    Q_OBJECT
 public:
     Virtual(QString name = "");
-    virtual ~Virtual(){};
+    virtual ~Virtual(){emit deleted();}
 
     enum class Type {
         Open,
@@ -48,6 +49,9 @@ public:
     QString getName() const;
     void setName(const QString &value);
 
+signals:
+    void deleted();
+
 protected:
     QString name;
     double minFreq;