The fix levels
With a receiver connected, the app names the fix level in plain words, with the technical term in brackets:
- Meter-level (standalone): satellites only, typically 1–3 m.
- Sub-meter (differential): corrections from SBAS or a base station, typically under a meter.
- Not yet fixed (RTK float): RTK in progress, decimeters at best.
- Centimeter-level (RTK fixed): RTK converged, typically 1–3 cm horizontally.
The phone's own GPS is usually good to a few meters under open sky.
The ± figure
With a receiver, the accuracy the app shows is the receiver's own estimate, taken from its GST messages: one sigma, so the true position is within that distance about two times in three. If the receiver doesn't send GST, the app says the accuracy is not reported. A fixed status alone doesn't guarantee a particular accuracy, so check the estimate, the base station distance and the sky as well.
Every GPS point keeps its accuracy. A GPS measurement's result shows its average and worst accuracy and how many samples were ignored, and the GPS quality requirement setting decides how strict that filter is.
Heights
Each point keeps the height the receiver reports. Technical details shows the altitude above sea level, the geoid separation and the ellipsoidal height. DXF exports keep each point's height as Z, in meters.
Coordinates and reference frames
The app stores latitude and longitude as the receiver reports them. Correction services use their own reference frames, so the same spot measured with two services can be about a meter apart even though both say centimeters. The app keeps each measurement on one correction source; for repeat work on a site, stay with one service.
Not a legal survey
Even with RTK, the app is a measuring and estimating tool. Do not use it to establish property lines, settle boundary disputes, or replace a licensed surveyor.