are we forgetting that the ASI is not a speed indicator at all .... only a differential pressure gauge ?... some assumptions and fancy designing labels the dial in speed instead of pressure ... if the conditions right here and now replicate the calibration assumptions then the gauge gives a correct speed .... at all other times it is wrong to a greater or lesser extent ... hence the various engineering tricks of different airspeeds to make the thing tractable for analysis .... worth reading the relevant sections of an engineering undergrad text on aerodynamics and the thing becomes a little easier to accept ..