error messages

Author: maxvhas

plot/waterfall.py

@@ -24,7 +24,7 @@ def __init__(self, filter_bank=None, center_freq=None, sample_freq=None,
             self.filter_bank = filter_bank
 
         if fig is None:
-            raise ValueError("Need figure.")
+            raise ValueError("A Matplotlib figure is needed to generate the plot.")
         else:
             self.fig = fig