I'm trying to figure out the 2 sec calc because today I got 7 readings in a row:
29.28
30.25
30.67
30.27
30.22
30.52
29.59
but my RealSpeed and KA72 2 sec peak is (http://www.ka72.com/TrackRecalc.aspx?fid=32417)
29.89

I found a post from TimeMachine (RealSpeed author): www.seabreeze.com.au/forums/Windsurfing/Gps/Bug-in-Real-Speed

40, 42, 43 (wishful thinking in these windless days I know...)

The two second result should be calculated as follows:
((40+42)/2 + (42+43)/2) / 2 = (41+42.5)/2 = 41.75

So mine would be
((30.25+30.67)/2+(30.67+30.27)/2)/2=(30.46+30.47)/2=30.465

Using GT31, latest firmware.

What am I missing? Something to do with Doppler?

Patrick,
Doesn't look right.

Check your Realspeed settings, see my post re: Realspeed Settings.

I would be interested to see your settings to compare.

Send me your track & I will check it.

Thanks Mark

In real speed the speed graph at the bottom can show both trackpoint and doppler lines in different colours.
(I think you right click in the bottom pane to select what's in there).
If you expand the 2s result out you can see the doppler data that's being used.
It's a pity the chart only shows trackpoint speed.

I'm fairly sure Paddymac meant when he made a 2 sec division based on trackpoints he got the same average from when he calculated by hand using the trackpoint data.

2 sec should definitely be doppler or select doppler if available.



Paddymac - right click over the track data, select grid fields, deselect speed and tick doppler. Do the same for distance and total doppler distance. In the graph window you can also right click for fields and turn on doppler.

Paul - Realspeed calculates the 2sec speed centred on the one second peak. So in the trackpoint sample Paddymac posted its saying he did 30.67 knots for 1 second, then it assumes 30.25 for half a second prior and then 30.27 for half a second after, so 2 seconds total. If you average just 2 numbers the average won't be centred on the peak, it will be off to one side of the peak.

sailquik said...

>>>

I am not sure what you mean by the chart only showing trackpoint speed. If you make a Doppler speed 2 sec division the speed shown is Doppler speed.

I'm not talking about the division results, and I'm not in windows so can't open real speed, only going by my failing memory here.
By "chart" I'm referring to the pane that shows, date, lat and long, total distance, total doppler distance, etc, and "speed" I haven't seen "doppler speed" there. If it had been paddymac wouldn't have been puzzled by unexpected results.

EDIT. just read Froude's message above, and it seems I haven't tried changing speed to doppler, next time I have realspeed open I'll have a look at that.