Imagine the first time you went out you powered it up at the trail head and it performed it's one time calibration there.CheminerWill wrote: ↑Wed May 08, 2019 5:15 amI can do that but if it is calibrating once upon starting up, should it not be correct for that whole power cycle? So if I power on the unit and do the first 1/2 of the track, it should be calibrated and correct on the elevation. If a week later I then power up and it does a calibration again, why would it be off from the first half? I must be missing how this works, but if it calibrates automatically each time it is powered on, why would that be a problem?gpsrchive wrote: ↑Wed May 08, 2019 3:41 am There you go. The GPSMAP 66 is auto calibrating 'Once' per power cycle, when the unit is first powered up. If you had performed a manual calibration at the point where you were starting the second half of the track recording, or performed a manual calibration at the exact same starting point from the first half, then moved to the second half before recording data, the elevation profiles likely would have been very similar.
But maybe the next time you went out you power it up in the vehicle getting to the trail head, and it is a hot day out and you have the windows up and the A/C on full blast....
Or, imagine each visit uses a different group of satellites, different days, different times, and one track log has many overhead satellites while the next has the majority of satellites closer to the horizon....
Or, maybe on Day one the sun is shining and the air is warm and dry, but on a follow up visit the clouds have moved in, the air is cool and damp...
So many variables for what really is an amateur hobbyist piece of equipment. These things are not professional surveyor grade scientific instruments.
If one wanted to make multiple tracks near the same location over multiple visits, one would be best served by choosing a common point near where the track log recordings were being done, and manually calibrating the unit to the same elevation for that point each time. Then the resulting recordings would all be centered off that one common point... a "Benchmark" if you will.... (wait, that sounds familiar)
8^)