Maker's Name: 
Edwards High Vacuum Ltd
Where made: 
27 × 16 × 7 cm

This consists of a heated filament which is cooled mainly by convection. This affects the temperature of the filament, and therefore the electrical resistance of the filament.

The filament forms part of a Wheatstone bride for determining the resistance, which is a measure of the vacuum in the gauge.

This gauge must be calibrated against a known vacuum using eg a McLeod gauge.

The gauge must be separately calibrated for different gases. Hydrogen removes heat rapidly, and the noble gases slowly.

This gauge is only suited to low vacuums.