diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index 27a28c85af8826e7cc625dd4b21fe4309fb4fce7..4ecfc38948bac9afc8fcec735253960a18069e7d 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -328,9 +328,8 @@ class OhmPiHardware:
         ax[3].plot(self.readings[v, 0], (self.readings[v, 2] * (self.readings[v, 4] - self.sp)) / self.readings[v, 3],
                    '-m', marker='.', label='R [ohm]')
         ax[3].set_ylabel('R [ohm]')
-        ax[4].plot(self.readings[v, 0], ((self.readings[v, 2] * self.readings[v, 4]) + self.sp) / self.readings[v, 3],
-                   '-m', marker='.', label='R [ohm]')
-        ax[4].set_ylabel('R [ohm]')
+        ax[4].plot(self.readings[v, 0], np.oneslike(self.readings[v,0] * self.sp), '-o', marker='.', label='SP [mV]')
+        ax[4].set_ylabel('SP [mV]')
         fig.legend()
         if save_fig:
             fig.savefig(f'figures/test.png')