What should one look for in the specifications to determine whether a handheld purpose-built GPS receiver provides good navigational consistency under reasonably normal, low-speed conditions? Highly preferably both in open areas as well as potentially dense woodland.
I am looking primarily for something that will work well for walking and bicycling (hence low-speed; good accuracy while travelling by car is less of a concern because then even a 15 meters error may translate to about half a second of travelling time).
Are marine units as a general rule better in this regard than (for want of a better word) "personal" GPS receivers, in the absence of an external antenna? Or are they simply more rugged, and certified for marine use, while providing little potential benefit to non-maritime users?
My current (admittedly somewhat dated) GPS receiver, even after having had plenty of time to download a full GPS almanac, with a clear view of the sky and half a dozen satellites to work with, often reports navigational accuracy to be in the range 10-20 meters. What's more, that number tends to vary quite wildly. That certainly is good enough to e.g. find one's way back to a known location such as getting back to the car or campsite, but as soon as you need more accuracy than that, it falls way short.
I will be using the receiver primarily within Scandinavia, and Sweden in particular, generally outside of cities and often in forested areas.
To clarify, it doesn't have to provide pin-point position accuracy (for that, 10-20 meters is very often quite sufficient), but consistency in readings in the same area is much more useful. As an example, if I lay down a track and then have the dog follow that track, I am very interested in how closely the dog actually follows the track but I am not particularly interested in the exact location of the track. So, if the readings are off by some reasonable distance that isn't a major concern (as has been pointed out, it's not like being 20 meters off means you are hopelessly lost; if it is, it's not like a GPS receiver is likely to help much); as long as that within a reasonably short time frame (more than minutes, less than hours) two readings taken in the same physical location match well in terms of the reported location, that's good enough for me.