diff --git a/Readme.md b/Readme.md
index 192e2c1..597a86a 100644
--- a/Readme.md
+++ b/Readme.md
@@ -14,7 +14,6 @@ Right now it depends on the following Python 3 libraries:
   * PIL (core library)
   * datetime (core library)
   * Image (core library)
-  * math (core library)
   * piexif
   * gpxpy
 
@@ -31,4 +30,7 @@ to-do
 
 ## future possibilities
 
-In the future it should also be able to do the same with a gpx-file to extract geolocations and to write them into the appropiate Exif-fields.
+  * In the future it should also be able to do the same with a gpx-file to extract geolocations and to write them into the appropiate Exif-fields.
+  * It might get interactive help and command line argument processing.
+  * It might get a setup.py if I want to waste my time on it.
+  * I might want to get rid of the requirement to use a bloated GUI application to download the history data off the geigercounter. There must be a neat working command line tool.
diff --git a/exif_rad.py b/exif_rad.py
index 4804996..7d31cf5 100755
--- a/exif_rad.py
+++ b/exif_rad.py
@@ -6,13 +6,20 @@ DateTimeOriginal from Exif tag to DateTime in a csv log
 of a GeigerMuellerCounter."""
 
 from datetime import datetime
+# import math
 from PIL import Image
-import math
 import piexif
 import piexif.helper
 
-# Constants
+# Constants for GQ geiger counters
+
+# 300  series: 0.0065   µSv/h / CPM
 # 320  series: 0.0065   µSv/h / CPM
+# 500  series: 0.0065   µSv/h / CPM
+# 500+ series: 0.0065   µSv/h / CPM for the first tube
+# 600  series: 0.0065   µSv/h / CPM
+# 600+ series: 0.002637 µSv/h / CPM
+
 SIFACTOR = 0.0065 
 
 # Temp constants