Just wondering how accurate are the gps speedo apps for smart phones? I use an iPhone and have a few different apps that I use but they seem to be all within a few 1/10ths of each other. Are the more expensive handhelds or the actual gps speedos more accurate?

I recently compared the gps app on my iPhone with the livorsi gps speedo in a boat and it was a spot on match.

I agree, my GPS speedo and iphone are almost dead on...

I have a mounted Garmin 440S, and a Navionics app on my iPhone. Speed results are pretty much the same. But the Navionics app is better on the chart, markers, and readability than my Garmin is. The Garmin cost 10 times more as well. I even have the extra 3D Blue card in the Garmin.