Crossfell Mk II Variometer System

I removed this Crossfell Mk. II Audio Variometer System from my vintage Phoebus A about 2 years ago. It was working fine when removed. The instrument requires a 4.5 volt battery, not included. Included is the early 1960's RAINCO advertising flyer that announced availability of this "state of the art" instrument. Also included are two pages of typed instructions for operation of the instrument and audio. This would make a great addition to a vintage glider.