compass declinometer

compass declinometer

[′käm·pəs ‚dek·lə′näm·əd·ər]
(engineering)
An instrument used for magnetic distribution surveys; employs a thin compass needle 6 inches (15 centimeters) long, supported on a sapphire bearing and steel pivot of high quality; peep sights serve for aligning the compass box on an azimuth mark.