diff --git a/Trajectories/cost_function.py b/Trajectories/cost_function.py
index 04f915f26f97ce3ffaf4f5bed30e33bb9b31eb9a..f7ef6da6e38d6eabb4ebc3c3a345501c31468d14 100755
--- a/Trajectories/cost_function.py
+++ b/Trajectories/cost_function.py
@@ -207,7 +207,7 @@ for n in g.vertices():
 
                 # We can use part of the properties from the beginning
                 # of the segment.
-                properties = properties[len_seg - n_days_avg :] + node_to_prop(
+                properties = properties[len_seg - n_days_avg:] + node_to_prop(
                     g.vp.inst_eddies[n][n_days_avg:],
                     g.gp.e_overestim,
                     SHPC,
@@ -248,7 +248,8 @@ for edge in g.edges():
     if first_av_ros[target_node] != 0 and last_av_ros[source_node] != 0:
         Delta_Ro = first_av_ros[target_node] - last_av_ros[source_node]
     else:
-        # At least one of the rossbies is invalid.
+        # At least one of the Rossby numbers (computed by
+        # calculate_radii_rossby) is invalid.
         Delta_Ro = 0
 
     # R_Vmax 1 and 2 already exist, just get the delta