Update README.md

README.md

@@ -18,7 +18,7 @@ collaborative work, see the AUTHOR file for details.
     * manuals: about "how to start" and " generate exe"  
     * descriptions/additional: background information documents 
     * descriptions/Fact_sheets: short summary of the model in English and German
-    * test_data_sets: test the propper working of the functions of the model with complete sets of data and control files 
+    * test_data_sets: test the correct function mode of the model with complete sets of input data and control files 
     * publications: all relevant publications regarding the model 4C
 
 The source code is distributed via a git repository at: