back staff

noun

1. an obsolete instrument for determining the altitude of the sun by facing away from the sun, sighting upon the horizon, adjusting a cursor until its shadow falls upon the sight through which the horizon appears, and measuring the resulting arc.

Word History and Origins

Origin of back staff¹

First recorded in 1620–30

Example Sentences

This instrument was known also as "the back-staff" from the position of the observer with his back to the sun when using it.

From Project Gutenberg