Determining differences of elevation with respect to a specified surface from differences of atmospheric pressure measured with a barometer or from differences of altitude determined using a barometric altimeter. By applying certain corrections and using what is sometimes called the barometric formula, a difference of atmospheric pressure at two places is transformed into a difference of altitude at those places. If the elevation of one station above a reference surface is known, the approximate elevations of other stations connected with it by barometric altimetry can be calculated. By using barometers of special design, and by including several stations of known elevation in a sequence of occupied stations, the accuracy of the elevations determined for the new stations is increased. Corrections are applied for temperature, latitude, index of barometer, misclosure of circuit, diurnal variation in atmospheric pressure, etc.