Re: GPS speed indications

Larry Sheldon wrote:
This is a pure question without preconceived notions as to what the answers might be.

What I think I know is that the unit-in-hand locates satellites and does timings to determine where it is in three dimensions.

What I don't know is how often they do that.

Seems like if the interval is very long it would not know about altitude changes, ziggy-zaggity twisty roads and while it would know position accurately it might not know exact distance traveled between fixes and thence would not be able to calculate speed accurately.

I don't exactly how often it updates. But I was watching my unit on two lane roads and freeways where the posted speed limit changes. My unit displays the road speed limit and dead on where the the posted speed limit was my unit showed the speed limit. This occurred numerous times. The only way it could know I was passing that point is by updating every half second or so.

Additionally my unit shows the speed I'm driving. As I adjust my speed the unit adjusts my speed almost immediately.

I'm guessing it updates its data 3-4 times per second