Thread: Accuracy figure of horizontal position fix on GPSMAP 66 satellite screen?

Apologies my typo and thanks for pointing it out, it was meant to say Multi-GNSS & I’ve corrected the post.

And this multi-GNSS aspect of the 66i is relevant to 65 & 66sr discussion:
1. The newer devices promote additional GNSS systems as one of the two new main features, and you have also stated the additional SV’s are “always better”. In my situation that has not shown to be the case so raises a question yet to be answered on the newer devices.
2. It also raises a question in the rigor of the estimated accuracy figure and how it is derived – the current topic.

If you have had different experiences and with one of the new devices please share it. And if you do be very careful how the datums are considered as this is another issue that directly relates to the topic of accuracy.

Garmin devices and software have very simplistic handling of map datums and do not accommodate all variables of plate movement, and particularly over time as everything is continually moving.

So ground coordinates you obtain from elsewhere or collect yourself will have already changed or will change position over time, and more importantly any datum transformations in the device will be further distorted by the simplistic transformation and the date for which it was set.

Normally this would not be an issue with consumer accuracies around 3 metres or more and Pro gear and software are designed to deal with it. However, with advancements in constellations and receiver’s Garmin is now nudging the boundary where these anomalies are relatively approaching similar magnitude and possibly now at times even the exceeding the displayed accuracy estimated in some areas.

As an example, we have recently updated our national datum here for GNSS consistency for the second time due to plate movement, this time the error difference was around 1.8m.

So for a device like the 66st which was estimating an accuracy of 1.8m this would be misleading and the reality with respect to the ground/map would actually be more like up to 3.6m.