The etrax is a older unit and at first would not read low speeds.
Garmin came up with a fix that was downloaded. One positive thing about Garmin is that they are always up dating their software.
I hope Lowrance gets on the stick soon.

I can see how it wouldn't be very accurate at slow speeds, but you'd think it'd give you a value, at least.

dtro:
Did you check to see if there were differences in the software versions on those two? and perhaps it was the older version that could display the readings below 1 mph?

I will check tonight.

Lowrance fixed mount gps that use the gps puck show speeds below 1.0 mph. This is just my opinion, but I think the accuracy of the antennas and receivers in the handhelds is not as good as the pucks - and not as good of accuracy means not as good at calculating speeds. That's probably why they don't show it below 1.0 mph on the handhelds.

I know that even at normal trolling speeds of 1.5 to 3.5 mph or so, my H20 speed reading jumps all over the place compared to my 332s speed readings.

dtro:
This begs a second question... was it a fixed mount system w/puck that showed the .6 mph reading and a handheld that read 0.00?

The strang thing is I run the year old H2O side by side with a seven year old garmin etrax. The garmin tracks down to 0.1 mph. Both use built in antennas. Go figure.
(IMHO) I believe it has something to do with software.
I have a external antenna for the H2O and when I get time I will check out the antenna thing.

Some GPSs seem to cut off at 1.0 mph. my old magellan did that. My 332 doesn't. I don't think my go2 does either. I always thought it was a software thing to keep the speed from jumping around while you are standing still.

I think you are correct. A gps doesn't automatically know the speed, it has to be programmed to calculate the speed, and programmed to display the speed. Not long ago there was a post where someone thought his earlier generation handheld was more accurate than the newer ones because the speed didn't jump around so much --- it wasn't more accurate, it was programmed to not update the speed calculation and display as frequently to prevent the jumping around ---- exactly what you mention in your post.

That's why adding an external antenna to a H2O won't make a difference --- the unit may have a more accurate reading of where it is and how fast it's moving, but if it's not programmed to calculate or display that, it won't matter.