diff --git a/ohmpi/ohmpi.py b/ohmpi/ohmpi.py
index 98f04d6505b8041d1739a1c854b5d0a6e55cd172..23603598bef70f53045c4e43cb4e591d38f18bb0 100644
--- a/ohmpi/ohmpi.py
+++ b/ohmpi/ohmpi.py
@@ -704,8 +704,8 @@ class OhmPi(object):
             if self._hw.tx.voltage_adjustable:
                 voltage = self._hw.tx.voltage  # imposed voltage on dps
             else:
-                voltage = d['Vmn [mV]']
-            current = d['I [mA]']
+                voltage = self._hw.rx.voltage
+            current = self._hw.tx.current
 
             # compute resistance measured (= contact resistance)
             resist = abs(voltage / current) / 1000.