circumferentor

[ser-kuhm-fuh-ren-ter]

noun Surveying.

an alidade equipped with a compass and two diametrically opposed vertical arms with slits for sighting through.

Origin of circumferentor

1600–10; < Latin circumferent(ia) circumference + -or²

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

An improvement which was no doubt introduced at a very early day is the measuring wheel or circumferentor.
The Seven Follies of Science [2nd ed.]
John Phin