ESDU 87038 describes the ground calibration tests made to the actual pressure measuring system as installed in the aircraft in order that corrections to flight measured air data for acoustic and viscous lag may be based on good empirical results. The ground tests are made for ranges of pitot and static pressures appropriate to the capabilities of the test aircraft. When the pressure system may be treated as first-order, methods are given for estimating the lag. When it must be regarded as being of second-order, calibration is essential and the use of three input pressure variations is considered: sinusoidal, ramp, and step. Two worked examples illustrate the use of the methods.