Historical information

This instrument measures elevation by sensing minute changes in barometric air pressure relative to a fixed datum point at sea level or a known elevation, such as the starting point of a major town during a road survey, and has an accuracy of +/- 20 feet when used in experienced hands.
The finely divided scale around the perimeter of the face is marked from 0 to 6000 feet elevation and 25 to 31 inches of mercury (Hg) for barometric pressure
The single fine counter-balanced hand or pointer rotates anti-clockwise with increasing elevation and decreasing pressure.
The label "compensated" indicates that the instrument is constructed to compensate for the effect of temperature changes on the accuracy of readings.

Physical description

Surveyor's Pocket Altimeter - Aneroid Barometer Type
Branded N H Seward, Melbourne. Made in England.
With leather carrying case and strap.