Reset reference on the combined logmag chart fixed

NanoVNASaver/Chart.py

@@ -1874,6 +1874,11 @@ class CombinedLogMagChart(FrequencyChart):
         self.reference21 = data21
         self.update()
 
+    def resetReference(self):
+        self.reference11 = []
+        self.reference21 = []
+        self.update()
+
     def resetDisplayLimits(self):
         self.reference11 = []
         self.reference21 = []

NanoVNASaver/RFTools.py

@@ -127,11 +127,14 @@ class RFTools:
     def groupDelay(data: List[Datapoint], index: int) -> float:
         idx0 = clamp_value(index - 1, 0, len(data) - 1)
         idx1 = clamp_value(index + 1, 0, len(data) - 1)
-        delta_angle = (data[idx1].phase - data[idx0].phase)
+        delta_angle = data[idx1].phase - data[idx0].phase
+        delta_freq = data[idx1].freq - data[idx0].freq
+        if delta_freq == 0:
+            return 0
         if abs(delta_angle) > math.tau:
             if delta_angle > 0:
                 delta_angle = delta_angle % math.tau
             else:
                 delta_angle = -1 * (delta_angle % math.tau)
-        val = -delta_angle / math.tau / (data[idx1].freq - data[idx0].freq)
+        val = -delta_angle / math.tau / delta_freq
         return val