Robust, especially cheap and for many years proven prism with nearly indestructible tilt holder made of plastic, which performs consistently for the harsh conditions in tunnel and monitoring purposes.

 
The centering of the prism is within 2 tenths of a millimeter. Robust clamp screw for the vertical axis, the unintentional rotation of the prism effectively prevented. The mounting of the tilt axis is deliberately kept too tight to avoid accidental tipping.