diff --git a/measure.py b/measure.py
index b90645c33e738c1851db26d191e6d608e8a591f2..7a7674612246e3dfd609ed9c28c9a3149c69a0e7 100644
--- a/measure.py
+++ b/measure.py
@@ -53,6 +53,7 @@ class OhmPiHardware:
 
     def _clear_values(self):
         self.readings = np.array([])
+        self._start_time = None
 
     def _inject(self, duration):
             self.tx_sync.set()
diff --git a/test_measure_with_ohmpi_card_3_15.py b/test_measure_with_ohmpi_card_3_15.py
index ff3080984fff1a65b0ab5a7f13d9bad45fde41a0..a0d5722015b90526806d6d7c23633f50467545f4 100644
--- a/test_measure_with_ohmpi_card_3_15.py
+++ b/test_measure_with_ohmpi_card_3_15.py
@@ -22,6 +22,8 @@ print(r)
 print(f'length of array: {len(r)}, expected length: {6000./k.rx.sampling_rate}')
 print(k.readings)
 fig, ax = plt.subplots()
-ax.plot(k.readings[:,0], k.readings[:,1], '-r')
-ax.plot(k.readings[:,0], k.readings[:,2], '-b')
+ax.plot(k.readings[:,0], k.readings[:,1], '-r', label='iab')
+ax2 = ax.twinx()
+ax2.plot(k.readings[:,0], k.readings[:,2], '-b', label='vmn')
+plt.show()
 change_config('config_default.py', verbose=False)