Large aneroid pocket barometer having 2½” French silvered and engraved dial, the outer rotating altimetric scale calibrated in feet with a range from 0 – 20000ft and divided to 100ft on the nonlinear Aires Scale, the barometric scale calibrated in inches of mercury with a range from 15” – 31” divided to 1/20^th”, the upper part marked “Compensated,” the lower with retailer’s details. Fine blued steel pointer, bevelled glass. Conventional improved Vidi pattern movement, dated “18/8/92,” driven from a single capsule tensioned on a C spring. All contained within a lacquered brass drum form case, calibration port to verso. Case extension and suspension ring.

All contained within its original brown leather over timber green velvet and silk lined case, snap closure on a button release.

Condition: The subject of a full service, conservation and calibration under laboratory conditions. Overall good, very minor marks to dial, the movement working exceptionally well with a high level of accuracy across and well below the standard barometric range, losing accuracy at lower pressure, higher altitudes consistent with age and design of instrument.

Comments: Early aneroid altimeters are always very interesting – this one with its wide range and retailer is of particular interest and must be considered extremely rare.

The firm of CG Spencer & Son was established in 1881, and a very interesting history of this famous family of balloon manufacturers and pilots can be read here.

For the collector of early aneroid instruments and aviation instruments alike.