When the external pressure drops, aneroid capsule 1 expands and, by means of tie-rod 2, turns shaft 3 with segment gear 4. Segment gear 4 turns pinion 5 which is secured to large gear 6, meshing with pinion 7. Large hand 8 is rigidly mounted on the shaft of pinion 7. Hand 8 makes one revolution per 1000 m altitude. Hand 9, driven through a train of gears, 15, 14, 17 and 16, with a gearing ratio of 10 : 1, makes one revolution per 10 000 m. A uniformly graduated scale is obtained by the provision of spring counterbalance 10 whose elasticity compensates for the nonlinear deformation of the capsule by the varying air density. The hands are set by knob 11 which turns plate 12 on which gears 14 and 17 are mounted. At the same time, the pinion of knob 11 turns scale 13, indicating the barometric pressure.
$3938$LHP,M$