This chapter describes the relationships between stagnation and static properties in compressible flow. It starts with an introduction including definitions of stagnation and static properties in Sect. 3.1. Section 3.2 derives the equations for stagnation–static relationships in terms of temperature, pressure, density, and Mach number, for isentropic flow. This section also clarifies the applicability of such relationships in non-isentropic flows. Isentropic flow tables along with relevant resources are introduced in Sect. 3.3. Section 3.4 derives the equation for mass flow rate in compressible flow in terms of Mach number, static, and stagnation properties. The relationship between stagnation pressure and entropy is examined in Sect. 3.5. Section 3.6 is an extensive section on air velocity measurements and calculations and starts with basic definitions and relationship between stagnation, static, and dynamic pressures. This section also includes the analysis and use of Pitot tube and Pitot static tube. Drag force in compressible flow and calculation of drag force experienced by aircrafts is also covered in Sect. 3.6. Section 3.6 also includes compressible equivalent of Bernoulli’s equation, speed measurements of aircrafts, aircraft speed terminologies, and air property variations with altitude. Section 3.7 looks at flow measurements including applications of venturimeter and orifice meter in compressible flow situations.