diff --git a/Software/PC_Application/CustomWidgets/informationbox.cpp b/Software/PC_Application/CustomWidgets/informationbox.cpp
index 20a4882..0713a06 100644
--- a/Software/PC_Application/CustomWidgets/informationbox.cpp
+++ b/Software/PC_Application/CustomWidgets/informationbox.cpp
@@ -20,6 +20,32 @@ void InformationBox::ShowMessage(QString title, QString message, QString message
     }
 }
 
+bool InformationBox::AskQuestion(QString title, QString question, bool defaultAnswer, QString messageID)
+{
+    // check if the user still wants to see this message
+    unsigned int hash;
+    if(messageID.isEmpty()) {
+        hash = qHash(question);
+    } else {
+        hash = qHash(messageID);
+    }
+
+    QSettings s;
+    if(!s.contains(hashToSettingsKey(hash))) {
+        auto box = new InformationBox(title, question, hash, nullptr);
+        box->setStandardButtons(QMessageBox::Yes | QMessageBox::No);
+        int ret = box->exec();
+        if(ret == QMessageBox::Yes) {
+            return true;
+        } else {
+            return false;
+        }
+    } else {
+        // don't show this question anymore
+        return defaultAnswer;
+    }
+}
+
 InformationBox::InformationBox(QString title, QString message, unsigned int hash, QWidget *parent)
     : QMessageBox(parent),
       hash(hash)
diff --git a/Software/PC_Application/CustomWidgets/informationbox.h b/Software/PC_Application/CustomWidgets/informationbox.h
index 0b06ca8..45f897f 100644
--- a/Software/PC_Application/CustomWidgets/informationbox.h
+++ b/Software/PC_Application/CustomWidgets/informationbox.h
@@ -8,6 +8,8 @@ class InformationBox : public QMessageBox
     Q_OBJECT
 public:
     static void ShowMessage(QString title, QString message, QString messageID = QString());
+    // Display a dialog with yes/no buttons. Returns true if yes is clicked, false otherwise. If the user has selected to never see this message again, defaultAnswer is returned instead
+    static bool AskQuestion(QString title, QString question, bool defaultAnswer, QString messageID = QString());
 private:
     InformationBox(QString title, QString message, unsigned int hash, QWidget *parent);
     ~InformationBox();
diff --git a/Software/PC_Application/Traces/tracexyplot.cpp b/Software/PC_Application/Traces/tracexyplot.cpp
index fbd58b6..647814a 100644
--- a/Software/PC_Application/Traces/tracexyplot.cpp
+++ b/Software/PC_Application/Traces/tracexyplot.cpp
@@ -153,9 +153,9 @@ void TraceXYPlot::fromJSON(nlohmann::json j)
     auto xtype = jX.value("type", XAxisType::Frequency);
     auto xmode = jX.value("mode", XAxisMode::UseSpan);
 //    auto xlog = jX.value("log", false);
-    auto xmin = jX.value("min", 0);
-    auto xmax = jX.value("max", 6000000000);
-    auto xdiv = jX.value("div", 600000000);
+    auto xmin = jX.value("min", 0.0);
+    auto xmax = jX.value("max", 6000000000.0);
+    auto xdiv = jX.value("div", 600000000.0);
     setXAxis(xtype, xmode, xmin, xmax, xdiv);
     nlohmann::json jY[2] = {j["YPrimary"], j["YSecondary"]};
     for(unsigned int i=0;i<2;i++) {
diff --git a/Software/PC_Application/VNA/vna.cpp b/Software/PC_Application/VNA/vna.cpp
index 393c708..6422a73 100644
--- a/Software/PC_Application/VNA/vna.cpp
+++ b/Software/PC_Application/VNA/vna.cpp
@@ -53,6 +53,7 @@ VNA::VNA(AppWindow *window)
     calValid = false;
     calMeasuring = false;
     calDialog.reset();
+    calEdited = false;
 
     // Create default traces
     auto tS11 = new Trace("S11", Qt::yellow);
@@ -104,10 +105,13 @@ VNA::VNA(AppWindow *window)
         } else {
             ApplyCalibration(cal.getType());
         }
+        calEdited = false;
     });
 
     connect(saveCal, &QAction::triggered, [=](){
-       cal.saveToFile();
+        if(cal.saveToFile()) {
+            calEdited = false;
+        }
     });
 
     auto calDisable = calMenu->addAction("Disabled");
@@ -508,6 +512,16 @@ void VNA::deviceDisconnected()
     defaultCalMenu->setEnabled(false);
 }
 
+void VNA::shutdown()
+{
+    if(calEdited && calValid) {
+        auto save = InformationBox::AskQuestion("Save calibration?", "The calibration contains data that has not been saved yet. Do you want to save it before exiting?", false);
+        if(save) {
+            cal.saveToFile();
+        }
+    }
+}
+
 nlohmann::json VNA::toJSON()
 {
     nlohmann::json j;
@@ -798,6 +812,7 @@ void VNA::StartCalibrationMeasurement(Calibration::Measurement m)
         // enable calibration measurement only in transmission callback (prevents accidental sampling of data which was still being processed)
         calMeasuring = true;
     });
+    calEdited = true;
 }
 
 void VNA::ConstrainAndUpdateFrequencies()
diff --git a/Software/PC_Application/VNA/vna.h b/Software/PC_Application/VNA/vna.h
index e0968dc..e5d67ec 100644
--- a/Software/PC_Application/VNA/vna.h
+++ b/Software/PC_Application/VNA/vna.h
@@ -19,6 +19,7 @@ public:
     void deactivate() override;
     void initializeDevice() override;
     void deviceDisconnected() override;
+    void shutdown() override;
 
     // Only save/load user changeable stuff, no need to save the widgets/mode name etc.
     virtual nlohmann::json toJSON() override;
@@ -67,6 +68,7 @@ private:
     // Calibration
     Calibration cal;
     bool calValid;
+    bool calEdited;
     Calibration::Measurement calMeasurement;
     bool calMeasuring;
     bool calWaitFirst;
diff --git a/Software/PC_Application/appwindow.cpp b/Software/PC_Application/appwindow.cpp
index 8d0a635..ccee4f9 100644
--- a/Software/PC_Application/appwindow.cpp
+++ b/Software/PC_Application/appwindow.cpp
@@ -184,6 +184,9 @@ AppWindow::~AppWindow()
 
 void AppWindow::closeEvent(QCloseEvent *event)
 {
+    vna->shutdown();
+    generator->shutdown();
+    spectrumAnalyzer->shutdown();
     delete device;
     QSettings settings;
     settings.setValue("geometry", saveGeometry());
diff --git a/Software/PC_Application/mode.h b/Software/PC_Application/mode.h
index 0aa4f08..931c5ae 100644
--- a/Software/PC_Application/mode.h
+++ b/Software/PC_Application/mode.h
@@ -17,6 +17,7 @@ public:
 
     virtual void activate(); // derived classes must call Mode::activate before doing anything
     virtual void deactivate(); // derived classes must call Mode::deactivate before returning
+    virtual void shutdown(){}; // called when the application is about to exit
     QString getName() const;
     static Mode *getActiveMode();