diff --git a/simulation_TREPR.m b/simulation_TREPR.m
index 24dc2b8..07d01b1 100644
--- a/simulation_TREPR.m
+++ b/simulation_TREPR.m
@@ -1,7 +1,19 @@
 function [params] = simulation_TREPR(params)
-%SIMULATION_TREPR Summary of this function goes here
+%SIMULATION_TREPR uses esfit to perform fitting of TREPR simulation
 %
-%   Detailed explanation goes here
+%   Usage: [params] = SIMULATION_TREPR(params), where params is a struct
+%   created by the PRE_SIMULATION_TREPR function.
+%   
+%   This function will show the mean of maxima, specified in the
+%   NORMALIZE_DATA function and allow inputs for Variation limits of
+%   relevant parameters for the simulations and for fitting options.
+%   "Start Fit" will call esfit and perform the specified fitting. For
+%   possible values, please refer to the easyspin docs.
+%   "Save Parameters" will write the current best fitting simulation
+%   parameters as starting values for a possible next iteration of fitting
+%   and also write them to the params struct. The button may only be
+%   pressed after performing at least one iteration of fitting.
+%   "Done" will close the window.
 
 %% setup
 %create struct for passing data between callbacks