Here's an interesting one. I noticed today, the GT31 was giving me a better alpha for yesterday than the GW52 did, so I did some investigating and found this sdop display in GPSResults, have used this before but it clearly demonstrates how accurate the GW52 can be worn on the head.
GT31 is the top display, GW52 is underneath.
The top GT31 alpha is number two for the GW52, and the sdop dots show why. The dots show the margin of error, this is very big during the gybe entry of the GT31, but the margin of error for the GW52 is so close to the reported speeds it's very hard to see.
The fact that the GT31 was on my arm, and the GW52 on my head, could be a factor.