ETA / time to go estimation calcs
Posted: Wed Sep 02, 2026 7:48 pm
I suspect this is a general GPSMAP 6x issue, not just a 66i issue, but it wasn't obvious how to make a more general post...
I have always been puzzled how the GPSMAP 66st (and now 66i) estimates how much time to the next waypoint and destination. I have always assumed it is some sort of average of the speed over the last X km or X minutes.
Yesterday, I used a new profile for the first time. I called it "Boat" and configured it for "direct" navigation, and had the gpsr aboard a ferry. Even thought the ferry sat constantly at about 30kph for a 45km trip, the initial estimate to destination was about 12 hours! Even after an hour's travel, the estimate was still many hours when we had less than 1/2 hour to go.
I couldn't find anything in the configuration that might have guided the unit in its calculations.
In the absence of people knowing for a fact how this is calculated, I would be interested in people's educated theories.
I have always been puzzled how the GPSMAP 66st (and now 66i) estimates how much time to the next waypoint and destination. I have always assumed it is some sort of average of the speed over the last X km or X minutes.
Yesterday, I used a new profile for the first time. I called it "Boat" and configured it for "direct" navigation, and had the gpsr aboard a ferry. Even thought the ferry sat constantly at about 30kph for a 45km trip, the initial estimate to destination was about 12 hours! Even after an hour's travel, the estimate was still many hours when we had less than 1/2 hour to go.
I couldn't find anything in the configuration that might have guided the unit in its calculations.
In the absence of people knowing for a fact how this is calculated, I would be interested in people's educated theories.