diff --git a/doc/source/pythonmodule.rst b/doc/source/pythonmodule.rst
index 58a309e..bc5e42a 100644
--- a/doc/source/pythonmodule.rst
+++ b/doc/source/pythonmodule.rst
@@ -30,6 +30,11 @@ The simulation loaders
 .. autofunction:: loadGadget
 .. autofunction:: loadParallelGadget
 
+Grafic Input and Output
+-----------------------
+
+.. autofunction:: readGrafic
+
 Timing
 ------
 
diff --git a/python/cosmotool/grafic.py b/python/cosmotool/grafic.py
index 65ac6c1..4ea6f9b 100644
--- a/python/cosmotool/grafic.py
+++ b/python/cosmotool/grafic.py
@@ -2,7 +2,20 @@ import struct
 import numpy as np
 
 def readGrafic(filename):
-
+  """This function reads a grafic file.
+  
+  Arguments:
+    filename (str): the path to the grafic file
+    
+  Returns:
+    a tuple containing:
+      * the array held in the grafic file
+      * the size of the box
+      * the scale factor
+      * the mean matter density :math:`\Omega_\mathrm{m}`
+      * the dark energy density :math:`\Omega_\Lambda`
+      * the hubble constant, relative to 100 km/s/Mpc
+  """ 
   with file(filename, mode="rb") as f:
         p = struct.unpack("IIIIffffffffI", f.read(4*11 + 2*4))
         checkPoint0, Nx, Ny, Nz, delta, _, _, _, scalefac, omega0, omegalambda0, h, checkPoint1 = p