Undercarriage Deflection Pressure Gauge, Defiant MK.I. Alloy, approx. 17 x 17cm when fully extended. Marked with callibrations for pressure from 215 to 700 lbs/square inch. Undercarriage height is the distance between the lowest point of the landing gear (bottom of the tyre) and the attachment point to the aircraft. When landing this distance decreases as the tyre compresses and any shock absorbing within the gear reacts.
This simple tool was presumably used to measure the deflection of the landing gear to assess the amount of 'travel' at given levels of pressure, allowing for adjustment where necessary. Various indistinct numbers and inspection stamps marked to rear 'BP91012 E70' ? Shows use and wear but in good condition overall. Stock code M18965.