diff --git a/Python_script/analysis.py b/Python_script/analysis.py
index 0d20ffeed20010795d88c6f5e9f19e96f5f2fbdf..775833e738fd0822c83c164586c905ad6603c693 100644
--- a/Python_script/analysis.py
+++ b/Python_script/analysis.py
@@ -77,9 +77,9 @@ def plot_sweep(temperatures, humidities, basename, sweep_type, measurement_sets,
     for measurement_set in measurement_sets:
         data = set_data[measurement_set]
         if analysis_config['normalise'][0]:
-            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]:
-            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])