THE fact that the engine power in full‐throttle flight is governed by thermodynamic conditions involving the atmospheric pressure and temperature at the air intake; while the engine power in throttled flight is, by adjustment of the throttle position, entirely at the choice of the pilot, is the cause of certain fundamental differences in the correction of full‐throttle and throttled tests to standard conditions. For, whereas full‐throttle flight, in which the aerodynamic forces are subject to a thermodynamical limiting condition, involves both aerodynamics and thermodynamics, throttled flight is purely aerodynamic. A simple illustration is provided by throttled level flight in which the throttle is adjusted until the airscrew thrust is equal to the drag at the air speed selected by the pilot; that is, the engine power is fixed by aerodynamic conditions alone.