diff --git a/sw/airborne/subsystems/ahrs/ahrs_float_dcm.c b/sw/airborne/subsystems/ahrs/ahrs_float_dcm.c
index 0af2996e16..70268a0100 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_float_dcm.c
+++ b/sw/airborne/subsystems/ahrs/ahrs_float_dcm.c
@@ -14,6 +14,7 @@
 
 /** \file ahrs_float_dcm.c
  *  \brief Attitude estimation for fixedwings based on the DCM
+ *  Theory: http://code.google.com/p/gentlenav/downloads/list  file DCMDraft2.pdf
  *
  */
 
diff --git a/sw/airborne/subsystems/ahrs/ahrs_float_dcm.h b/sw/airborne/subsystems/ahrs/ahrs_float_dcm.h
index d088612961..5ffb38854b 100644
--- a/sw/airborne/subsystems/ahrs/ahrs_float_dcm.h
+++ b/sw/airborne/subsystems/ahrs/ahrs_float_dcm.h
@@ -14,6 +14,7 @@
 
 /** \file ahrs_float_dcm.h
  *  \brief Attitude estimation for fixedwings based on the DCM
+ *  Theory: http://code.google.com/p/gentlenav/downloads/list  file DCMDraft2.pdf
  *
  */