Last week, while on vacation, I decided to use my Garmin 10 on a couple of dayhikes just to see how far we were hiking and what the elevation gain was.  I found it really frustrating.  The watch's auto-pause kept turning off and on, even though I was still moving.   Maybe it was because I was walking slowly (hiking with dog plus DH has bad knees), maybe because the terrain was in a narrow canyon with dense tree cover, but it made for some weird results.  The 'moving time', 'elapsed time' and 'actual time' were over an hour different.  Because the climb was steep, and in places there were a lot of switchbacks, the mileage was also way off.

I probably won't be using it again while hiking, but it made me wonder about its accuracy while trail running.  Do any of you find that your Garmins get really inaccurate on trails?

Mine has always been fine on trails... though sometimes it will say lost GPS signal on trails with lots of hills and stuff.

It could have been an off day.  One day the satellites were so bad that my Garmin was auto-pausing for me during a track workout!  Talk about feeling slow!  I have only used it on a few trail runs, but it seemed to work pretty well for me on the trails.  We weren't that far out, though, and tree cover wasn't super heavy.

Hmm, I must not use auto-pause. I get reasonable distance estimates although elevation might be 10+% high. There is a setting to help distinguish motion from randomly having satellite think you are moving - I think it's the minimum pace you want considered as moving. On our big mountains - 3000ft up in 2.2 mi with some stretches near 50+% slopes - my gps frequently thinks I'm stopped. I *know* I wasn't stopped that long. But the amount of up and distance are reasonable when I'm all done. I use it on all my runs and many hikes (might use my handheld gps in some cases).

My garmin usually measure trail courses short due to all the switch backs, the tree cover might hinder it a bit as well. I don't use the auto pause feature so I have never had it act up like you described.

I turned on my Auto-Pause feature when I got my Garmin, but honestly I think it's helped once and hindered a half dozen times. So I'll probably turn it off. I'm in the habit of pausing my Garmin when I hit a stoplight or something.

There is a setting to help distinguish motion from randomly having satellite think you are moving - I think it's the minimum pace you want considered as moving.

That is a good point, I remember setting that on mine now that you mentioned it.

I turned off auto pause after my first run with my new Garmin (my 305 didn't have it).  It seemed like it took 5-10 seconds to figure out I had started running again.  I just manually stop and start it at stop lights.  It has become a habit anyways.  I used the watch on an H3 run where half the run was wading through thigh high water in stream beds in the jungle and it seemed pretty accurate even though I was moving pretty slow.  I haven't done another one of those runs though.  One was enough.

Can't remember if my auto pause is off or if I set the minimal pace to 12:00 min/mile................ right now I am just too lazy to check though.

I turned mine off after only a few uses when my numbers started looking odd. I had it set at 20:00 and it still paused when I was moving along at a pace twice as fast as that.