diff --git a/Readme.md b/Readme.md
index bb745fd..604f1e2 100644
--- a/Readme.md
+++ b/Readme.md
@@ -32,10 +32,12 @@ These exported .his files look like this:
 ## Usage
 
 ```
-usage: exif_rad.py [-h] [-si SIFACTOR] [-o OUTDIR] CSV Photo [Photo ...]
+usage: exif_rad.py [-h] [-si SIFACTOR] [-tz Timezone] [-d] [-g GPX]
+                   [-o OUTDIR]
+                   CSV Photo [Photo ...]
 
-A tool that writes radiation levels (and optionally geocoordinates) to image
-files and extracts the infos from external sources.
+A unix-tyle tool that extracts GPS and/or radiation data from GPX/CSV files
+and writes them into the Exif tags of given photos.
 
 positional arguments:
   CSV                   Geiger counter history file in CSV format.
@@ -46,8 +48,15 @@ optional arguments:
   -si SIFACTOR, --sifactor SIFACTOR
                         Factor to multiply recorded CPM with. (default:
                         0.0065)
+  -tz Timezone, --timezone Timezone
+                        Manually set timezone of CSV / and Photo timestamp,
+                        defaults to localtime if omitted. (default: None)
+  -d, --dry             Dry-run, do not actually write anything. (default:
+                        False)
+  -g GPX, --gpx GPX     GPS track in GPX format (default: None)
   -o OUTDIR, --outdir OUTDIR
-                        Directory to output processed photos (default: .)
+                        Directory to output processed photos. (default: .)
+
 ```
 
 ### Examples
diff --git a/exif_rad.py b/exif_rad.py
index 8c5277c..d5bd091 100755
--- a/exif_rad.py
+++ b/exif_rad.py
@@ -31,9 +31,10 @@ parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFo
     them into the Exif tags of given photos.''')
 parser.add_argument('-si', '--sifactor', type=float, default=0.0065, 
                     help='Factor to multiply recorded CPM with.')
-parser.add_argument('-tz', '--timezone', type=str, metavar='Timezone',
+parser.add_argument('-tz', '--timezone', type=str, metavar='Timezone', default='utc',
                     help='''Manually set timezone of CSV / and Photo timestamp,
-                    defaults to localtime if omitted.''')
+                    defaults to UTC if omitted. This is useful, if the GPS-Logger
+                    saves the time incl. timezone''')
 parser.add_argument('-d', '--dry', action='store_true', 
                     help='Dry-run, do not actually write anything.')
 parser.add_argument('csv', metavar='CSV', type=str,