diff --git a/sw/airborne/math/pprz_algebra_int.h b/sw/airborne/math/pprz_algebra_int.h
index 0a410b2e6a..f8cc0c926a 100644
--- a/sw/airborne/math/pprz_algebra_int.h
+++ b/sw/airborne/math/pprz_algebra_int.h
@@ -182,6 +182,7 @@ struct Int64Vect3 {
 };
 
 
+// Real (floating point) ->  Binary Fixed Point  (int)
 #define BFP_OF_REAL(_vr, _frac)    ((_vr)*(1<<(_frac)))
 #define FLOAT_OF_BFP(_vbfp, _frac) ((float)(_vbfp)/(1<<(_frac)))
 #define RATE_BFP_OF_REAL(_af)   BFP_OF_REAL((_af), INT32_RATE_FRAC)