Repurposed Barometer
Aircraft Altimeters are actually Barometers that are calibrated to represent each change of 27 millibars as a 100' height change. The reference pressure is set using the knurled knob to the lower left of the instrument and the reference pressure is on the right. This pictures was taken at 2850 feet above Pontypridd on Sunday. The reference pressure (the pressure at Sea Level at Cardiff), referred to by pilots as the QNH, was 1024 mBar, seen in the small window on the right hand side of the display.
Repurposed Barometer
Aircraft Altimeters are actually Barometers that are calibrated to represent each change of 27 millibars as a 100' height change. The reference pressure is set using the knurled knob to the lower left of the instrument and the reference pressure is on the right. This pictures was taken at 2850 feet above Pontypridd on Sunday. The reference pressure (the pressure at Sea Level at Cardiff), referred to by pilots as the QNH, was 1024 mBar, seen in the small window on the right hand side of the display.