This early instrument consists of a large brass compass box with a graduated circular scale and a pair of sight vanes mounted on a single piece of metal. Surveyors mounted it on a Jacob's staff or tripod to read magnetic bearings for mapping and boundary lines. It was the primary tool for laying out large tracts of land before the transit and theodolite became common.
Heard on the job
The original colonial boundaries were run using a circumferentor, which explains why the magnetic bearings drift so much compared to our GPS coordinates.
Also heard as
- surveyor's compass