# On station adjustment

From the Settings screen use the On station adjustment option to control the position that will be measured when the tunnel surface does not match the design, that is, the surface is in either underbreak or overbreak.

Refer to the following diagram and table that illustrates an underbreak situation.

1 | Instrument position | 5 | Measured position when On station adjustment is selected
2 | Tunnel surface | 6 | Measured position when On station adjustment is not selected
3 | Tunnel design | 7 | Design position
4 | Station | 8 | Horizontal alignment

The overbreak is similar to the underbreak situation.