keef said...thanks decrep and karl, there is a difference the navelink is
---MAX SPEEDS---
[ 1] 31.33 KTS
[ 2] 31.17 KTS
[ 3] 30.77 KTS
[ 4] 29.11 KTS
the 2 sec is 28.89 and the bottom grid is 29.14 theres no track and no doppler , i guess my settings are wrong so ill have have a fiddle and try and work it out, i allwas was a slow learner

OK that navilink stuff is the display speeds, they're virtually instantaneous.
To get a proper 2s average 3 adjacent readings need to be averaged, so will be up to a knot less.
Not sure what you mean by the bottom grid, the bottom grid on what???
Trackpoint and doppler is the way you set up realspeed, for a GT31 everything should be calculated in doppler.
trackpoints will give you a higher result, but doppler is more accurate.