Distance measurement 
When measurements are being made using the red laser EDM, the results can be influenced by objects passing between the EDM and the intended target surface. This occurs because reflectorless measurements are made to the first surface returning sufficient energy to allow the measurement to take place. For example, if the intended target surface is the surface of a building, but a vehicle passes between the EDM and the target surface as the measurement is triggered, the measurement may be made to the side of the vehicle. The result is the distance to the vehicle, not to the surface
of the building.
If using the long range measurement mode (> 1000 m, > 3300 ft) to prisms, and an object passes within 30 m of the EDM as the measurement is triggered, the distance measurement may be similarly effected due to the strength of the laser signal.
Very short distances can also be measured reflectorless in Reflectorless mode to well reflecting natural targets. The distances are corrected with the additive constant defined for the active reflector.
Due to laser safety regulations and measuring accuracy, using the Long Range Reflectorless EDM is only allowed to prisms that are more than 1000 m (3300 ft) away.
Accurate measurements to prisms should be made in prism mode.
When a distance measurement is triggered, the EDM measures to the object which is in the beam path at that moment. If a temporary obstruction, for example a passing vehicle, heavy rain, fog or snow is between the instrument and the point to be measured, the EDM may measure to the obstruction.
Do not measure with two instruments to the same target simultaneously to avoid getting mixed return signals.
ATR/lock
Instruments equipped with an ATR sensor permit automatic angle and distance measurements to prisms. The prism is sighted with the optical sight. After initiating a distance measurement, the instrument sights the prism centre automatically. Vertical and horizontal angles and the distance are measured to the centre of the prism. The lock mode enables the instrument to follow a moving prism.
As with all other instrument errors, the collimation error of the automatic aiming must be redetermined periodically. Refer to "5 Check & Adjust" about checking and adjusting instruments.
When a measurement is triggered while the prism is still moving, distance and angle measurements may not be made for the same position and coordinates may vary.
If the prism location is changed too quickly, the target may be lost. Make sure that the speed does not exceed the figure given in the technical data.