diff --git a/dev/test_2_mux_2024.py b/dev/test_2_mux_2024.py
index c51a7ca748842fad821cb8d1603026d8fd32b110..48e3f2890dc1966a6bdec626a2ec6487e17d7a36 100644
--- a/dev/test_2_mux_2024.py
+++ b/dev/test_2_mux_2024.py
@@ -49,8 +49,8 @@ if within_ohmpi:
     k._hw.vab_square_wave(3.,1)
     k._hw.switch_mux([1, 4, 2, 3], state='off')
     k._hw.calibrate_rx_bias()  # electrodes 1 4 2 3 should be connected to a reference circuit
-    print(f'Resistance: {k._hw.last_rho :.2f} ohm, dev. {k._hw.last_dev:.2f} %, rx bias: {k._hw.rx._bias:.2f} mV')
-    k._hw._plot_readings()
+    # print(f'Resistance: {k._hw.last_rho :.2f} ohm, dev. {k._hw.last_dev:.2f} %, rx bias: {k._hw.rx._bias:.2f} mV')
+    # k._hw._plot_readings()
     k._hw.switch_mux([1, 4, 2, 3], state='on')
     k._hw.vab_square_wave(3.,1)
     k._hw.switch_mux([1, 4, 2, 3], state='off')
diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index f9baa2856e42539fe17ca325ea5c3ee2acece5d0..335e56cd73e5684609ddef6f41859dc7acc7aba3 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -204,15 +204,17 @@ class OhmPiHardware:
 
     @property
     def last_rho(self):
-        if len(self.readings) > 1:
-            return np.mean(np.abs(self.readings[:, 4] - self.sp) / self.readings[:, 3])
+        v = self.readings[:, 2] != 0
+        if len(v) > 1:
+            return np.mean(np.abs(self.readings[v, 4] - self.sp) / self.readings[v, 3])
         else:
             return np.nan
 
     @property
     def last_dev(self):
         if len(self.readings) > 1:
-            return 100. * np.std(self.readings[:, 2] * (self.readings[:, 4] - self.sp) / self.readings[:, 3])/self.last_rho
+            v = self.readings[:,2] != 0
+            return 100. * np.std(self.readings[v, 2] * (self.readings[v, 4] - self.sp) / self.readings[v, 3])/self.last_rho
         else:
             return np.nan