For straight tunnels up to 400 m:
In order to eliminate refraction influences acting to the laser beam as tunnel length increases, the U.N.S. Guidance System is supplemented with a hydrostatic water level to calculate a more accurate vertical machine position.
For long distance and curved tunnels:
A north-seeking gyrocompass is installed in the TBM, which does not need a line of sight to the launch shaft. This allows a precise calculation of the horizontal position of the machine. The vertical deviation of the TBM position from the designed tunnel alignment is calculated using the integrated hydrostatic water level system.