When using a GPS question in Magpi the app will save the accuracy value, as well as latitude and longitude. That value is also displayed to the mobile user:
If the accuracy is 16.28, that is meant to convey that the current location is within 16.28 meters of the acquired latitude and longitude. A larger accuracy number means a less accurate set of GPS coordinates.
For a more technical discussion of GPS accuracy:
https://stackoverflow.com/questions/10634734/what-does-horizontalaccuracy-exactly-mean