diff --git a/quality.c b/quality.c
index 3a3ee85..7e44354 100644
--- a/quality.c
+++ b/quality.c
@@ -1,5 +1,7 @@
 #include "imuread.h"
 
+// Discussion of what these 4 quality metrics really do
+// https://forum.pjrc.com/threads/59277-Motion-Sensor-Calibration-Tool-Parameter-Understanding
 
 //static int countdown=1000;
 //static int pr=0;