There is still a serious problem with the GT-31 and Alphas. I had two GT-31's on for testing today but I had to post my GT-11 speeds. The Alphas I got from the GT-31 were ridiculous and obviously erroneous when you look at the speed graph. One GPS said 27.980 and the other said 28.952!!!! I was pretty startled by the numbers at first glance but one look at the graph showed all sorts of strange bumps in the wrong places. I thought Tom had taken 'Smoothing' off in the newer GT-31 firmware but it certainly does not appear to be the case from these results. On the test firmware I tested with Tom recently with 'smoothing' OFF, the results were extremely good and very close to the GT-11 trackpoints with no strange bumps in the graph. These results done with the latest firmware were just plain wrong. If you are using a GT-31 for Alphas and that is all you have, the only thing I can suggest is that you use Doppler for the Alphas but that will be handicapping yourself with the current firmware. If you are serious about Alphas, please use a GT-11 and trackpoints, or even a Garmin for that.
The GT-11 gave me a new PB with 27.898 and a clean graph with no bumps like this:



The GT-31 gave me this with a very strange and false speed graph (shown here with the Doppler graph in green for comparison)



I will follow this issue up again with Tom and Locosys.

Thanks Andrew, there's obviously something weird going on there.
The filtering seems to want to cancel the min speed dip out.

BTW off topic, I was watching my gybes today, (not thinking about them, just watching what my feet do) and unexpectedly, my front foot goes in first.