diff --git a/pre_simulation_TREPR.m b/pre_simulation_TREPR.m
index e2a9c4c..c7a882c 100644
--- a/pre_simulation_TREPR.m
+++ b/pre_simulation_TREPR.m
@@ -1,6 +1,14 @@
-function [Exp,Sys,params] = pre_simulation_TREPR(dataIN,params)
-%PRE_SIMULATION_TREPR Summary of this function goes here
-%   Detailed explanation goes here
+function [Exp,Sys,params] = pre_simulation_TREPR(params)
+%PRE_SIMULATION_TREPR allows manual fitting of parameters in GUI
+%
+%   Usage: [Exp,Sys,params] = PRE_SIMULATION_TREPR(params), where params is
+%   a struct, created by the load_bruker/matlab function and preprocessed
+%   by NORMALIZE_DATA, at least.
+%
+%   The function will show a window with a plot of the normalized mean of
+%   maxima (calculated by NORMALIZE_DATA) and serveral input fields for
+%   different relevant paramters of TREPR fitting. By pressing "Apply" the
+%   simulation will be calculated and displayed.
 
 %% creating UI
 fig = figure;