diff --git a/README.md b/README.md
index b04bc7f..f0ad0aa 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,49 @@
 # PM100_waist
 
 Make your waist measurment easy with a Thorlabs PM100D.
+
+## Setup
+```
+==============================
+Prepare the setup
+==============================
+laser             PM100D
+-->------------------] in W
+        |
+        |
+        |
+
+ knife at z and x=0mm
+
+==============================
+move the knife and press enter
+==============================
+laser             PM100D
+-->-----|------------] in W
+        |
+        |
+
+ knife at z and x+=0.05mm
+
+==============================
+```
+
+## Acquisition
+`pm100d_waist.py` acquire the optical power along transverse section at *z* mm.
+
+Create your measurement folder
+`mkdir -p my/best/measurement && cd my/best/measurement`
+
+Run the acquisition program with the `-o` option to set z=123mm as terminaison of the filename.
+All the files will be saved in the current folder
+`path/to/the/program/location/pm100d_waist.py -o 123`
+
+Press *enter* to get a power value, and move the knife of 0.05 mm, repress enter and again and again and again and again and again and again...
+When the section is done, enter the new z value in the prompt, the program will inform you that a new file is created.
+
+At the end, press `CTRL + C` and enter to quit *properly*.
+
+## Post-processing
+`fit_waist.py` fit each waist of each section and compute the *w0* and the *z0* of the beam.
+
+`./fit_waist.py`