Garmin GPSMAP 62S problem

There are a couple of reasons for this inaccuracy. Firstly, GPS drift while stationary causes the Trip Odometer to record track points continuously even though the unit is stationary. You can see this on Basecamp where you stop for lunch and there is a tight knot of track points around that location. Theses erroneous track points should be deleted in Basecamp to improve the accuracy of the calculated track distance. The only fix for this while on the trail is to turn the GPS unit off while stopped for any length of time, like at lunch time, then turn it on again once you start walking again.

The second source of error is caused by the frequency of the track point recording in Trip Odometer. The GPS unit takes a track point every second that the unit is turned on, which is way too frequent for the speed that it is moving if it is being used for hiking. At normal walking speeds of about 4 km/hr, a person will only walk about 0.8 metres per second, which is much smaller than the GPS unit's accuracy of +/- 3.0 metres, so the trip odometer is recording a lot of track points all around the actual location due to drift, which adds a lot of erroneous distance to trip odometer. To get a more accurate calculation of distance on the trail, Garmin would need to change the location sampling frequency to once every 5-10 seconds so the actual distance walked is 4 to 8 metres between track points. There is no solution to this design flaw in the Garmin GPS units. I have found that the trip odometer distance is about 8-10% greater than the actual distance, so I just discount the trip odometer distance by 10% to get a more accurate estimate of the distance walked while on the trail.

You need to know that the Trip Odometer and track log are not the same data. The Track Log is filtered using the settings in the GPS unit, so it only records a small portion of the track points recorded by the Trip Odometer. You don't see the same track points the Trip Odometer is using to calculate distance walked unless you setup the unit to record track points every second. Also, the distance that the Track Log shows in Basecamp when you first download the track file to Basecamp is reported from summary data that is in the Track File that comes from the Trip Odometer when the GPS unit creates the Track File, which is overstated by at least 10%. If a single point is deleted in Basecamp, Basecamp recalculates the distance for the hike using the track points in the track log and deletes the summary data section in the Track File, which will provide a more accurate distance walked.

I summary, the distance reported by the trip odometer in the Garmin GPSMAP 64 units will always be inaccurate due to a couple of design flaws: track point sample rate of one every second is way too high, and stationary drift is not filtered. Always turn the unit off while stationary for any period of time, and discount the Trip Odometer distance by 10%. An accurate estimate of the distance walked will only be available once the Track File has been filtered in Basecamp.

Unless yours is different you can set your Garmin to create track points based on distance rather than time. This may suit you better when you're hiking. Doing it by time is more suited when using it on a bike or in a car.

I tend to switch my gps off when I stop for a reasonable length of time.

Unlike you though I do find the distance remarkable accurate. Twice now I've walked a long distance route that is 268 miles long. Both times my GPS has been within a few miles of that. To me that's pretty good.

As I explained in my original note, the settings in Track Manager only affect the number of track points that are put into the Track File. I have left my setting at Auto/More Accurate. It does not affect the number of track points that Trip Odometer is using to calculate the distance while on the trail, which is fixed at 1 second intervals, hence the inherent built-in over-statement of distance. if I look at a plot of a track file that was recorded with a one second interval in Basecamp, it looks like the teeth of a saw. After filtering the track file in Basecamp based on a distance of 2-3 metres, the track plot is more of a straight line and the calculated distance walked is shorter by about 10%.

As I said, I find mine amazingly accurate without the 10% error you quote, and note I am talking about trip odometer. Which software are you running? See the posts above.

Oddly, by comparing distances with other people while on the trails, the little Forerunner units that runners use are more accurate at reporting distance walked because the location sample rate is lower

This now has nothing to do with BaseCamp.