I purchased a Garmin
GNX20 with a Airmar DST800 paddlewheel speed sensor. I noticed that the boatspeed value is always 0.5/0.8 higher than the SOG (from my GPS).
When I tried to calibrate it, the menu says "bring the boat
to cruising speed, note down, stop and press ok". What I do is:
1) set the engine
at 1500 rpm
, so the gnx20 displays boatspeed 4.5 kts (sog 4kts)
2) I stop the boat
3) I press ok --> 4,5 value appears on screen
4) press ok --> "calibration error" appears on screen
What am I doing wrong? Thxs.