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GreenEgg said..
When 2 doppler devices are being being compared where one receives 12 satellites with a 0.8 Hdop and the other receives 16 satellites with a 1.6 Hdop ... which of of both devices will be most accurate ?
I think HDoP is a measure of positional accuracy not doppler speed accuracy. If you're interested in doppler speed accuracy you need to check SDoP or SAcc if it's a ublox device.
I've just checked a file with both HDoP and SDoP, when SDoP shows less accuracy the HDoP goes higher, so looks like the 1.6 is less accurate, for position, but that's not necessarily true for doppler speed.

So you can see by the track here an obvious spike, positional data says it's 29kts, doppler data says 15 knots.
HDoP is 2.4, SDoP is +/-1.67 kts. There will be a bit of correspondence between the two because they are both subject to the same bad satellite signals.
So the SDoP tells you the speed was 15.667 +/- 1.672Kts.
The positional data says it was 29.162 kts with HDoP of 2.4