Pressure coefficient  The pressure coefficient is a dimensionless number which describes the relative pressures throughout a flow field in fluid dynamics. The pressure coefficient is used in aerodynamics and hydrodynamics. Every point in a fluid flow field has its own unique pressure coefficient, formula_1. In many situations in aerodynamics and hydrodynamics, the pressure coefficient at a point near a body is independent of body size. Consequently, an engineering model can be tested in a wind tunnel or water tunnel, pressure coefficients can be determined at critical locations around the model, and these pressure coefficients can be used with confidence to predict the fluid pressure at those critical locations around a full-size aircraft or boat. The pressure coefficient is a parameter for studying both incompressible/compressible fluids such as water and air. The relationship between the dimensionless coefficient and the dimensional numbers is   where:  Using Bernoulli's Equation, the pressure coefficient can be further simplified for potential flows (inviscid, and steady):  where u is the flow speed at the point at which pressure coefficient is being evaluated, and Ma is the Mach number: the flow speed is negligible in comparison with the speed of sound. For a case of an incompressible but viscous fluid, this represents the "profile" pressure coefficient, since it is associated with the pressure hydrodynamic forces rather than the viscous ones. This relationship is valid for the flow of incompressible fluids where variations in speed and pressure are sufficiently small that variations in fluid density can be neglected. This is a reasonable assumption when the Mach Number is less than about 0.3.   formula_1 of minus one is significant in the design of gliders because this indicates a perfect location for a "Total energy" port for supply of signal pressure to the Variometer, a special Vertical Speed Indicator which reacts to vertical movements of the atmosphere but does not react to vertical maneuvering of the glider. In the fluid flow field around a body there will be points having positive pressure coefficients up to one, and negative pressure coefficients including coefficients less than minus one, but nowhere will the coefficient exceed plus one because the highest pressure that can be achieved is the stagnation pressure. In the flow of compressible fluids such as air, and particularly the high-speed flow of compressible fluids, formula_14 (the dynamic pressure) is no longer an accurate measure of the difference between stagnation pressure and static pressure. Also, the familiar relationship that stagnation pressure is equal to "total pressure" does not always hold true.