diff --git a/Python_script/analysis.py b/Python_script/analysis.py
index 84e91b2cd75f4f35a1b5471dbcb0a938b8f65fe4..e15e505c1c68a653a61846df5cc443a7737ae6c9 100644
--- a/Python_script/analysis.py
+++ b/Python_script/analysis.py
@@ -78,10 +78,10 @@ def plot_sweep(temperatures, humidities, basename, sweep_type, measurement_sets,
         data = set_data[measurement_set]
         if analysis_config['normalise'][0]:
             if data['signal0_means']:
-                data['signal0_means'] -= data['signal0_means'][0]
+                data['signal0_means'][:] = [x - data['signal0_means'][0] for x in data['signal0_means']]
         if analysis_config['normalise'][1]:
             if data['signal1_means']:
-                data['signal1_means'] -= data['signal1_means'][0]
+                data['signal1_means'][:] = [x - data['signal1_means'][0] for x in data['signal1_means']]
 
     fig = plt.figure(figsize=(10, 15))
     gs = gridspec.GridSpec(nrows=6, ncols=1, hspace=0)#, width_ratios=[3, 1], height_ratios=[3, 1])