As the aircraft climbs, the diaphragm contracts and the pressure drops faster than the case pressure can escape through the restrictor, resulting in climb indications; the reverse is true during descent. If level flight is resumed, pressure equalizes in the case and diaphragm within six to nine seconds and the pointer returns to zero rate of climb. The vertical speed indicator has 100-ft calibrations with numbers every 500 ft (see Face of Vertical Speed Indicator figure below).