Distance dependant errors – but my prism type is correct
Leica’s range of total-station instruments have the option to apply a scale-factor to the EDM distance measurement. For small sites, where scale-factors are not used, this EDM-setting can be ignored (the default is 1.00). However, on those rare occasions when your free-station just doesn’t quite resolve to a few mil, or a known-backsight generates an incorrect distance, it is always worth checking the applied scale-factor is set as 1.00. Anything above/below will incur a range alteration, corrupting your position.
This is particularly common on Leica TS06 instruments, whereby the scale-factor infrequently changes to 0.99960 i.e. 40mm distance error (short) for a 100m baseline. Check the EDM / SCALE properties if this happens.