Before determining the instrument errors, the instrument has to be levelledup using the electronic level. Please refer to the Controller manual in order to use the electronic level. The tribrach, the tripod and the underground should be very stable and secure from vibrations or other disturbances.
The instrument should be protected from direct sunlight in order to avoid thermal warming. It is also recommended to avoid strong heat shimmer and air turbulence. The best conditions are usually early in the morning or with overcast sky.
Before starting to work, the instrument has to become acclimatised to the ambient temperature. Approximately two minutes per °C of temperature difference from storage to working environment but at least 15 min should be taken into account.
Note, that even after good adjustment of the ATR, the crosshairs might not be positioned exactly on the centre of the prism after an ATR measurement has been executed. This is a normal effect. To speed up the ATR measurement, the telescope is normally not positioned exactly on the centre of the prism. The small rest deviations, the ATR offsets are measured individually for each measurement and corrected electronically. This means that the Hz- and V- angles are corrected twice: first by the determined ATR errors for Hz and V and then by the individual small deviations of the current pointing.