diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1 +1,25 @@
-# allanplot
+# Description
+
+Compute and plot Allan Deviation from tab separated values files.
+
+# Usage
+
+`python allanplot.py --help`
+
+usage: allanplot.py [-h] [-f FILENAME] [-c COLUMNS [COLUMNS ...]] [-r RATE]
+
+Plot Allan Deviation from timeseries file
+
+optional arguments:
+  -h, --help            show this help message and exit
+  -f FILENAME           File(s) to import (default *.dat)
+  -c COLUMNS [COLUMNS ...]
+                        Columns to import (default 2)
+  -r RATE               Time rate in seconds (default 1)
+
+Example: './allanplot.py -f 'toto.dat' -c 2 3' compute and plot Allan
+Deviation form columns 2 and 3 of toto.dat
+
+# Examples
+
+`python allanplot.py -f '**/*.dat` will load all dat files in all sub-directories of the current path.