Altimeters measure the height above sea level by measuring barometric pressure. Altimeters and barometers are similar in that they both measure atmospheric pressure; however, an altimeter has additional functionality which allows pressure readings to be converted to altitude. An aneroid altimeter consists of a box or chamber partially exhausted of air, having an elastic top and a pointer to indicate the degree of compression of the top caused by the external air.

The Society has a number of different altimeters in its collection.