diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.cpp b/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.cpp
index 806a674..50f5e2b 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.cpp
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.cpp
@@ -15,6 +15,7 @@ Math::Expression::Expression()
 {
     parser = new ParserX(pckCOMMON | pckUNIT | pckCOMPLEX);
     parser->DefineVar("x", Variable(&x));
+    dataType = DataType::Invalid;
     expressionChanged();
 }
 
@@ -37,10 +38,8 @@ void Math::Expression::edit()
 {
     auto d = new QDialog();
     auto ui = new Ui::ExpressionDialog;
+    d->setAttribute(Qt::WA_DeleteOnClose);
     ui->setupUi(d);
-    connect(d, &QDialog::finished, [=](){
-        delete ui;
-    });
     ui->expEdit->setText(exp);
     connect(ui->buttonBox, &QDialogButtonBox::accepted, [=](){
         exp = ui->expEdit->text();
@@ -93,7 +92,7 @@ void Math::Expression::inputSamplesChanged(unsigned int begin, unsigned int end)
     data.resize(in.size());
     // sanity check input values
     if(end > 0 && end > in.size()) {
-        end = in.size() - 1;
+        end = in.size();
     }
     if(end <= begin) {
         dataMutex.unlock();
@@ -119,6 +118,14 @@ void Math::Expression::inputSamplesChanged(unsigned int begin, unsigned int end)
     emit outputSamplesChanged(begin, end);
 }
 
+void Math::Expression::inputTypeChanged(DataType type)
+{
+    // call base class slot
+    TraceMath::inputTypeChanged(type);
+    // we need to evaluate the expression again to create the correct variables
+    expressionChanged();
+}
+
 void Math::Expression::expressionChanged()
 {
     if(exp.isEmpty()) {
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.h b/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.h
index 39e8b2e..2c17698 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Math/expression.h
@@ -24,6 +24,7 @@ public:
 
 public slots:
     void inputSamplesChanged(unsigned int begin, unsigned int end) override;
+    virtual void inputTypeChanged(DataType type) override;
 
 private slots:
     void expressionChanged();
diff --git a/Software/PC_Application/LibreVNA-GUI/Traces/Math/tracemath.h b/Software/PC_Application/LibreVNA-GUI/Traces/Math/tracemath.h
index e99b4b1..e8a238e 100644
--- a/Software/PC_Application/LibreVNA-GUI/Traces/Math/tracemath.h
+++ b/Software/PC_Application/LibreVNA-GUI/Traces/Math/tracemath.h
@@ -130,7 +130,7 @@ public slots:
     // some values of the input data have changed, begin/end determine which sample(s) has changed
     virtual void inputSamplesChanged(unsigned int begin, unsigned int end){Q_UNUSED(begin) Q_UNUSED(end)}
 
-    void inputTypeChanged(DataType type);
+    virtual void inputTypeChanged(DataType type);
 
 signals:
     // emit this whenever a sample changed (alternatively, if all samples are about to change, emit outputDataChanged after they have changed)