diff --git a/ohmpi/hardware_components/dummy_ctl.py b/ohmpi/hardware_components/dummy_ctl.py
index 0e16923f47caacf915ea718db81d91434ea9af13..b9cedf8f4adfa133cad9bd57ccc5fa8e48f66531 100644
--- a/ohmpi/hardware_components/dummy_ctl.py
+++ b/ohmpi/hardware_components/dummy_ctl.py
@@ -8,4 +8,4 @@ class Ctl(CtlAbstract):
     def __init__(self, **kwargs):
         kwargs.update({'board_name': os.path.basename(__file__).rstrip('.py')})
         super().__init__(**kwargs)
-        self.bus = None
+        self.connections = None
diff --git a/ohmpi/hardware_components/dummy_tx.py b/ohmpi/hardware_components/dummy_tx.py
index 68bb4129548d4155be33305f25b540cd4e943661..067c1465978814876e4dba25e64f182b83d1d150 100644
--- a/ohmpi/hardware_components/dummy_tx.py
+++ b/ohmpi/hardware_components/dummy_tx.py
@@ -1,4 +1,4 @@
-from ohmpi.ohmpi.config import HARDWARE_CONFIG
+from ohmpi.config import HARDWARE_CONFIG
 import time
 import os
 import numpy as np
diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index b20587487e633e5919fb27a18a533105f4dc6197..f7934e54e216c1165e3aa41c7b20b791d4e1ac18 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -215,7 +215,7 @@ class OhmPiHardware:
     def last_dev(self):
         if len(self.readings) > 1:
             v = self.readings[:, 2] != 0  # exclude sample where the is no injection
-            return 100. * np.std(self.readings[v, 2] * self.readings[v, 4] / self.readings[v, 3]) / self.last_rho
+            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