diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index 0028e61b9f0479fe1f37b9fe8f8514ce6246db85..634e3b8c9db80efd1df1958952ed860a2081a0a8 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -296,9 +296,9 @@ class OhmPiHardware:
         x = []
         for pulse in range(int(max(self.readings[:, 1]))):
             v = np.where((self.readings[:, 1] == pulse))[0]
-
-            t_start_pulse = min(self.readings[v, 0])
-            x.append(np.where((self.readings[:, 0] >= t_start_pulse + delay) & (self.readings[:, 2] != 0) & (
+            if len(v) > 0:  # to avoid pulse not recorded due to Raspberry Pi lag...
+                t_start_pulse = min(self.readings[v, 0])
+                x.append(np.where((self.readings[:, 0] >= t_start_pulse + delay) & (self.readings[:, 2] != 0) & (
                         self.readings[:, 1] == pulse))[0])
         x = np.concatenate(np.array(x, dtype='object'))
         return x