diff --git a/src/main.cpp b/src/main.cpp
index c53e142..ddda516 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -551,7 +551,7 @@ void printHelp(bool error)
         << PACKAGE << " --help|-h\n\n"
 
         << "Options:\n"
-        << "-a period       Sets the length in seconds of the time window for average\n"
+        << "-a period       Sets the length in milliseconds of the time window for average\n"
         << "                calculation.\n"
         << "                Default is " << STANDARD_AVERAGE_WINDOW << ".\n"
         << "-i max_scaling  Specifies the 100% mark in kBit/s of the graph indicating the\n"