Question

what is altimeter? how its scale is calibrated?

Answer 1

An altimeter or an altitude meter is an instrument used to measure the altitudeof an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water.

Answer 2

When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter.An accuracy comparable with that of the ordinary scale calibration is desirable. It is the purpose of this paper to describe such a pressure standard, its use in calibrating altimeters