Geoffrey,
Yesterday I have tested your new alpha, F-GGH-2P-1201161.GHX, on a slow and well sick -flu- run.
First I used my old 625M belt and my 580p ant+ belt.
I did not notice any HR peaks like I used to. I brought with me 580p (like I always do but today with a double chest strap set up) and my friend's 405.
Every time I checked 580 and 625xt, they were always in perfect sync (+/-1bpm).
Here's the graph (average HR for 580p = 161, for 625xt = 162). I don't know why but overlay graphs do not work for me in the latest TGP, so I am sharing graph separately.
Also average distance in the lower right windows of TGP show no comma for 580p (25329km) but does for 625xt (25,55km). This seems to cause TGP to have some problems to display 580p activity/training graph properly in the overlay section.580p

625xt

As for the 405 I did not know you had to have the ant stick to upload data and I just have usb cable. Doh...
And I did not set HR in my user field so I don't know how to check average HR in my historic, so I'll it go.
BTW bezel does not work super dooper in cold weather.
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Today I had fever so I decided to test new 625XT HR belt along ant+ belt on a small run around the corner (with the new alpha firmware).
Not long, but I think it's enough to see that the new 625xt belt seem to be the problem as mentioned here by Hubert:
http://www.usglobalsat.com/forum/index.php?topic=3982.msg11436#msg11436580 time base and distance base
625xt time base and distance base

I took a least one minute without moving before starting to run and did the same after the run.
So my conclusion is that I do suspect intermittent or bad contact/solderings into the new belt electrodes. Could someone check soldering if there is? I can check resistance next week if I have time but would like to see a schematic of how it's done inside.
My hypothesis goes in the same way than Ander's remark about moving or not for bpm precision: not moving = better contact, moving = increase bad contact.
PS
Partyman and Longjog, I deleted my old thread
Eureka: HR problem solved! including your posts to not induce people in error and make them think that the problem was solved. Hope it does not matter with you...
And my apologies for having confused anyone with my old and new belt mistake. They look so much the same when there is not much light ;-)
canadien