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

There is no confusion between the 66i and 66sr, to be clear I have used the 66i as an example as I have actual experience with one and it helps to illustrate to both the market segment positioning of these devices and more significantly gives an example of a relatively new multi-GNSS unit that in my heavily forested environment here has tested less accurate than an older device.

In case you missed it my Rino 650 is GPS only, and it demonstrates less multipath and better point accuracy than the multi-GNSS 66i with GPS & Galileo. Regardless of the estimated accuracy number displayed. I wish it was not the case.

So twice as many SV’s whilst highly desirable are not “always better”, it depends on how good the device is and what it does with them. There is often a difference between simplistic theory and hype and actual real-world performance in specific conditions.

With the 65 & 66sr I would hold off regurgitating the “exceptional multi-path rejection” and “significant step forward” superlatives until I actually had one in my hands and properly tested it.

Dual frequency is not new, I've had in my Trimble devices for decades and it definitely helps. However, the devices have to make certain calculations and assumptions so it is not perfect and there are also many more factors than ionosphere at play. Hence even that device is geared for differential correction.

Reviews of the 66sr & 65 I have seen to date indicate the improvements are clearly there but are incremental rather than earth shattering, and as the mood here suggests that whilst nice to have don’t really provide a significant benefit for most people.

Interestingly in one example a GPSMAP65s reviewer noted that the track improvements were more significant in urban environment than forest, and in southern Californian forest actually recorded some instances of the 65s tracks noticeably in error compared to a number of older units. So whilst not a scientific review there is some similarity to my experience with the 66i and the 65 & 66sr may also not be perfect in these environments. [Only registered and activated users can see links. ]

And a general practical note regarding accuracy, don’t get overly hung up and forget that any underlying maps also have an error and particularly so with the growing trend to utilizing open-source data including Topo Active. This data has not been collected to any standard, and almost certainly not with accurate mapping devices. Forest tracks can also deviate over time. So for many common usage situations a 25% or better device accuracy could be somewhat irrelevant. E.g. you might now see with 25% greater confidence that the track on the map is around 30m in error….