diff --git a/apps/dedreckon/README.md b/apps/dedreckon/README.md
index e46c6fd69..706c7f191 100644
--- a/apps/dedreckon/README.md
+++ b/apps/dedreckon/README.md
@@ -14,4 +14,7 @@ now). Point watch to new direction, then tap top left part of screen
 to indicate a turn.
 
 Map shows blue line for track from dead reckonging, and green line for
-track from GPS.
\ No newline at end of file
+track from GPS.
+
+You probably want magnav installed (and calibrated) for useful
+results, as it provides library with better compass.
\ No newline at end of file