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 installed on a glider, this is known without ambiguity as the '''variometer'''.
==== How to measure total energy ====
==== How As outlined above, the problem of total energy compensation boils down to measure the problem of finding a location on the aeroplane where the pressure coefficient is -1. This is, however, not easy. We can get around this problem by designing a device which '''produces''' this pressure coefficient, just like a pitot tube is designed to produce a pressure coefficient of +1. This device is known as a total energy tube or total energy ====probe. There are mainly two kinds of architectures: the Venturi type (found on HTV) and the cylindrical type (found on KFY, JEC, PZ, and some other gliders at GRL).
=== Variometer (gliders) ===