About 10m off

[sushiboy21]

I have a Garmin Summit HC which has always worked great, with very accurate readings. I recently erased all the POIs, tracks and waypoints.

 

Since then, I've been unable to find any caches as the readings all seem to be a bit off.

 

I tested with two waypoints I know precisely and my readings seem to be about 10 metres off, both with the compass on and off.

 

I'm using WAAS enabled and WGS84 as a my datum. I d/l the cache coordinates directly from geocaching.com to the Garmin.

 

Any ideas? I'm perplexed.

[jmundinger]

I have a Garmin Summit HC which has always worked great, with very accurate readings. I recently erased all the POIs, tracks and waypoints.

 

Since then, I've been unable to find any caches as the readings all seem to be a bit off.

 

I tested with two waypoints I know precisely and my readings seem to be about 10 metres off, both with the compass on and off.

 

I'm using WAAS enabled and WGS84 as a my datum. I d/l the cache coordinates directly from geocaching.com to the Garmin.

 

Any ideas? I'm perplexed.

 

I don't think clearing poi's, tracks and waypoints would have been the cause of your issue. I would use a benchmark or two to confirm that you have an accuracy issue. If you still think you have an issue, I'd start by removing and reinstalling the batteries (or, replace if the current set is not reasonably fresh) and then reacquire the almanac - turn the unit on, and, on the satellite page, select "new location" and leave the unit with a clear view of the sky for several minutes.

[+BlueDeuce]

You need to recalibrate the compass after every battery change. Not doing so can cause problems.

[+twolpert]

10m is probably acceptable error unless you absolutely know that the coordinates are correct. If you are dealing with cache coordinates, or coordinates of a point you marked yourself, you are dealing with two sources of error: the error in the original coordinates and the error in your current position. If these happen to be off in opposite directions (for example, original coordinates north of reality and your current position south of reality), then 10m is not at all unexpected -- or unacceptable.

 

Checking vs. a benchmark is good advice. That way, you only have one source of error -- your current position.

 

When doing this kind of repeatability experiment, be sure you allow the unit to "settle" for 90 seconds or so before taking a reading. Stand still and wait for 90 seconds, then check your coordinates. You may have to do this a couple of times as you approach the location to get the most accurate reading on "ground zero."

 

I doubt that this is an almanac issue, nor am I sure that selecting "new location" on this unit will reacquire the almanac (although that may well be true). In any case, it takes at least 12.5 minutes to download a complete almanac. Most folks recommend letting the unit sit for 20 minutes or so to be sure you get the complete almanac.

 

Bottom line: Unless you consistently (repeating the observation several times over several days, to eliminate issues related to the constellation at the time) get a large error vs. a known location (like a benchmark), you probably don't have a faulty unit.