In this image the Estimated horizontal accuracy is 11.2m i.e. there is only a 68% chance that this lat./long. is within 11.2m of the "real" location ! Even though the HDOP in this case is an apparently very good 0.8m and 20 satellites have been used to calculate this position. This is the instantaneous accuracy - this can be substantially improved by averaging.
So for this particular measurement, there was a 1/3 chance that the tag is more than 11m away from this GPS data shown by the phone. This is not good enough for finding cave entrances on the plateau (there are often half a dozen holes within 10m) and certainly no good for surveying.
The Help text in the app explains this in more detail. On the web read: Measuring GNSS accuracy on Android devices
Get the estimated horizontal accuracy of this location, radial, in meters.We define horizontal accuracy as the radius of 68% confidence. In other words, if you draw a circle centered at this location’s latitude and longitude, and with a radius equal to the accuracy, then there is a 68% probability that the true location is inside the circle.
TTFF is "time to first fix". This means I would have had to wait at least 2 seconds after stopping moving before I would have any hope that a photo taken with the camera on this phone would get an accurate fix embedded in it.
GPStest online documentation explaining all the information on the screen.
Image: Philip Sargent, 2026