This is a remarkable result. This implies that if we can monitor the pressure at a location X on the aeroplane such that \( C_{pX} = -1 \), we can track the total mechanical energy change of the aeroplane. This is the fundamental working principle of a "total energy compensated variometer". When a "variometer" is installed on a glider, this is known without ambiguity it usually refers to a compensated instrument as the '''variometer'''described above, although other types of compensation that shows other quantities of interest are available.