Definition

The determination of differences of ELEVATION from (a) vertical angles and horizon­tal distances, as in TRIGONO­METRIC LEVELLING; (b) compara­tive ELEVATIONS derived from values of ATMOSPHERIC PRESSURE deter­mined with a BAROMETER, as in BAROME­TRIC LEVELLING; and (c) ELEVATIONS derived from values of the boiling point of water determined with a HYPSOME­TER, as in THERMOMETRIC LEVELLING.