Geocaching with Colorado 400t

I find zereoing (closing) in on the cache from several different angles really helps. You also just cannot consider the accuracy of your GPS. Although there is no way to know... How far off was the person's GPS who placed the cache? What if they were at the edge of their 40 foot (or whatever) accuracy reading? Caches can be quite a bit off from the posted coordinates when you take into account the error in your GPS AND the error when placing the cache initially.

Good point about errors when the cache was first placed. Approaching the cache from different directions is helpful.

I just don't understand way the direction indicator (using the Geocaching profile) varies so much when getting close to the coordinates. It seems like the Colorado 400t should be guiding me consistantly to the coordinates entered, even if the coordinates are not the exact location of the cache.

What you are experiencing is a problem with the way bearing and distance errors are displayed. The direction error is angular and the indicator can swing wildly when you are near the destination. The distance error is linear so the "swings" are not so wild.

I spent a long time flying helicopters in the military and we experience similar errors in TACAN, inertial navigation, GPS, radar. The errors in your position relative to a waypoint are really exaggerated when you have a direction indication.

The strategy we used flying and i still use walking is to take a final look at the bearing indication when I am still a reasonable distance away (like 30 or 40 meters walking). I get a visual bearing of where I am heading and ignore the bearing indication from then on. I stop looking at the distance when I get to a relative minimum and start using my eyes and brain to resolve where I am supposed to be. That strategy has never failed me.

You're advocating common sense! Blasphemy!

Wait, I actually said that in print? Not sure what I was thinking.

It won't because your GPS position is updated once per second from burst transmissions sent from the satellites. So, say you have a +/- 30 foot error/accuracy reading. That is a SIXTY foot diameter circle centered on your position for THAT second. Pretty significant, right? Each future second that ticks by can theoritically "pop" you to any point inside that circle because it's within the claimed accuracy. And, you need to understand that every second when your position is updated on the GPS (you can see this when zoomed all the way in as "wandering"), that "error circle" is recentered every time...it moves on top of already being a significant error... If you really want to see this "wandering movement", turn the track log on and let it sit overnight. You'll see that track wander all over the place even though the GPS unit hasn't physically moved.

In this example, sixty feet in diameter may not sound like much until you figure the area in that circle via (Pi)(radius^2). So, (3.141597...)(30)(30) is almost 3000 square feet. That geocache can be anywhere inside the area of a pretty good sized single floor house! And the dead center of that house moves over the surface of the earth (thankfully, a VERY tiny amount) for every second update!

You have each offered some great insights. Thanks to you all. Now that I understand what is happening a bit better, things start to make sense. I don't have to be concerned that there is problem with my particular unit.

You have been very helpful!