postprocessing-output-data.md

 Postprocessing functions available
 
+# Extract one time step from a compressed/archived file
+
+A function in slimPost is able to extract one time step from an archived/compressed file.
+
+Useful import
+
+```python
+import slimPost
+```
+
+This function needs the path to the archive file, the path to the variable you want to extract in the archive, the index of the time step you want to extract, the file format (msh or vtk) and the path to the directory where the file(s) will be extracted.
+
+```python
+slimPostextract_one_time_step("myArchive.tar", "output/sw2d/eta", 200, "msh", "my_new_dolder", export_all=False)`
+```
 # Particle tracker
 
 SLIM is able to predict the position of one (or several) particle(s) from the hydrodynamic output.