Drift Sight, Mk II-C Pelorus, with Recording Base, WWII US Navy Aircraft
Here is an early WWII-era US Navy aircraft Pelorus Drift Sight. A Pelorus Drift Sight is designed to function either as a Pelorus, for taking bearings on objects, or for improving dead reckoning aircraft navigation by measuring the angle between the heading and the track of an airplane. It consists of a small 'telescope' viewing vertically towards the ground, angled toward the direction of the aircraft. When viewing the ground through the scope while in flight, the navigator observes the travel of fixed objects across the lens. By rotating the scope on its base to align the path of these objects, the drift angle is determined by reading the location of the pointer on the base's scale. Once done, the course correction is calculated and communicated to the pilot.
The Mark II-C consists of an Optical Head, an upright post, and a Recording Base. The Optical Head features 3 interchangeable lenses to mitigate the view amid bright sun or cloud and smoke cover. It also has an illuminated reticle projected onto the sight from below, powered by a D-cell battery, that lights upon depressing the silver button at the top, and had a rheostat to adjust its brightness. The electrical circuit and bulb have been tested and they do work (please provide your own battery). The Optical Head and post were made by Maxwell Smith Co.
The Recording Base contains paper to record drift markings over time, so that the average drift can be calculated. It contains a winding mechanism that will advance the paper automatically as the drift is marked. The Recording Base was made by Waltham Watch Co.
This example is in terrific condition given its age. Measures ~16 inches tall, base is ~7 x 3 x 4 inches, and the scope is ~5 x 4 x 3 inches.