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→How to measure total energy
The drawback of a Venturi in measuring the total energy is that it is not tolerant to yaw. Most of the time when the total energy will be of interest is when the glider is soaring, and continuous turning is usually included in this process. If the glider has some yaw, the air will not enter the Venturi in the correct direction but it needs to turn a bit. This changes the pressure in the Venturi and leads to unreliable readings. A more benign design is the cylinder type.
[[File:cylinder_total_energy_tube.png|200px|thumb|right|Schematic of a cylindrical total energy tube]]
A schematic drawing of a cylindrical type of total energy tube is also presented<ref>https://crgis.ndc.nasa.gov/crgis/images/7/7e/PEN00109.pdf</ref>. These resemble closely the total energy tubes found on gliders today. The working principle of these tubes is not trivial and a theoretical approach to the design of these is not available to the author's knowledge. Qualitatively, these rely on the low pressure found in the wake behind the cylinder created by the separation of the boundary layer. In 1976 NASA did extensive experiments on these devices and the optimal geometry was found and presented in the Technical Memorandum X-73928<ref>https://crgis.ndc.nasa.gov/crgis/images/7/7e/PEN00109.pdf</ref>.
=== Variometer (gliders) ===