This  landing compass will give very accurate directional readings and is extensively used by Military and Civil aircraft operators for setting up Navigation Instruments during Aircraft swinging.
The compass is of a sturdy brass construction. Readings are obtained by looking through a fixed prism in conjunction with the opposite sighting vane. They can be supplied to give actual magnetic headings, or reciprocal readings and come complete with Stowage Box, Plumb Bob and Deviation Card. This specific compass was used at  "Soesterberg" military airport.