Figure 4-21.  A variometer diaphragm anatomy. Figure 4-22.  Uncompensated variometer in level flight.  Figure 4-23.  Uncompensated variometer in a climb. 4-12 4 6 8 10 4 6 8 10 Static pressure inlet Linkages and gearing : Connects the diaphragm capsule to the display needle. Capacity flask: A rigid, thermally insulated flask (similar  to an insulated beverage container). Capillary hole : A small hole in the diaphragm capsule designed to allow the pressure inside the  capacity flask to slowly equalize (within a  few seconds) with the atmospheric pressure air in the main body of the instrument. Diaphragm capsule : A capsule with elastic properties. Like a plastic  water bottle, it expands if the pressure inside is  greater than the pressure outside. It compresses if  the pressure outside it is greater than the pressure  inside it. 0.5 liters (approx.) Vertical speed:  Indicated in knots of vertical  climb and descent.  4 6 8 10 4 6 8 10 900 mb Local atmospheric pressure  at 3,000 feet 900 mb 900 mb 900 mb Altitude 3,000 feet level flight In level flight, the pressures throughout  the variometer and capacity flask  equalize to the local atmospheric  pressure at the flight altitude via the  static vents. 1 There is no difference between  the pressure inside and the pressure  outside the diaphragm capsule. 2 The capsule is neither compressed nor  inflated, and the display needle points  to zero. 3 Vertical speed indicated in knots  4 6 8 10 4 6 8 10 894 mb Local atmospheric pressure  at 3,500 feet Pressure falling from 900 mb to 884 mb  as altitude increases 892 mb 894 mb 892 mb Altitude 3,500 during climb from 3,000 feet to 4,000 feet As a glider climbs, the atmospheric  pressure around the glider falls. 1 The pressure inside the variometer’s  case matches this pressure drop  almost instantaneously. 2 The pressure of the air inside the capacity flask takes several seconds to catch up because it must  vent through the small capillary hole. 3 During a climb, the pressure inside the  capacity flask and diaphragm  capsule is slightly higher than the pressure inside the variometer’s case. The diaphragm capsule expands,  rotating the display needle to show  an increasing altitude. 4