diff --git a/communication_techniques/src/main.c b/communication_techniques/src/main.c
index f8aa110..ed3cfe8 100644
--- a/communication_techniques/src/main.c
+++ b/communication_techniques/src/main.c
@@ -48,7 +48,7 @@ void usage(char *argv[])
 		"Facultative options :\n"
 		"-h\t\t\tPrint this help\n"
 		"-s\t\t\tShare the same L2 cache or not\n"
-		"-c calculation_libname\tLibrary to use for calculation\n"
+		"-c calculation_libname arg\tLibrary to use for calculation with its argument\n"
 		"\t\t\tThis library must implement functions in calc.h\n";
 	printf("Usage : %s %s\n", argv[0], format);
 	printf("Options :\n");