diff --git a/seagraph.py b/seagraph.py
index ee86a3c..2d4e4ab 100644
--- a/seagraph.py
+++ b/seagraph.py
@@ -7,6 +7,15 @@ import json
 import numpy as np
 
 class PrettyFloat(float):
+    """saves bandwidth when converting to JSON
+
+    a lot of numbers originally have a fixed (low) number of decimal digits
+    as the binary representation is not exact, it might happen, that a
+    lot of superfluous digits are transmitted:
+
+    str(1/10*3) == '0.30000000000000004'
+    str(PrettyFloat(1/10*3)) == '0.3'
+    """
     def __repr__(self):
         return '%.15g' % self
 
@@ -24,6 +33,7 @@ class Scanner(object):
         self.test_day = test_day
     
     def scan(self, variable, timerange, result):
+        """return value is true when there are aditionnal points after the time range"""
         start, to, now = get_abs_time(timerange + [0])
         old = None
         t = 0