For monitoring and other applications where repeat measurements are required, it is sometimes not practical to mount an array of expensive prisms. In these circumstances, a GMP105 (page 93 of catalogue) can be manually held up against a reference nail and measured by a Total-Station. The constant for this is +40.0mm, using the screw-thread extension at the back of the prism. Create a new prism with a 40mm “Add Constant”.

*ensure the prism is held perpendicular to the wall, as the rotation centre is ~22.5mm forward of the reference point*

 

GMP111 prism constant:             +17.5mm

GMP111-0 prism constant:         0.0mm

GMP105 Prism, set against pt: +40.0mm