Compound curve

A curve formed in more than one plane. The surface of a sphere is a compound curve. Compound gauge (air conditioning servicing equipment). A pressure gauge used to measure the pressure in the low side of an air conditioning system. A compound gauge is calibrated from zero to 30 inches of mercury vacuum, and from zero to about 150-psi positive gauge pressure.

Aviation Maintenance Technician Handbook — Airframe, p. G-9