This traditional instrument features sighting slits or prisms set exactly at right angles to each other. A surveyor places it on the main traverse line and looks through the sights to guide a rodman into a position exactly ninety degrees to the side. It was heavily used for taking lateral offset measurements to irregular boundaries like rivers or fences.
Heard on the job
Grab the optical cross from the truck so we can lay out these building grid offsets.
Also heard as
- cross-staff
- optical square