Altimeter
is an instrument that measures the height of the land surface or any object
such as an airplane. The most common types of altimeters are barometric. They
determine altitude by measuring air pressure. As altitude increases, air
pressure decreases. This is because the density of air is lower at high
altitudes. Altimeters are important navigation instruments for aircraft and
spacecraft pilots who monitor their height above the Earth’s surface. Skydivers
and mountaineers also use altimeters to pinpoint their location in the sky or
on the ground.