eckhard
Actually the ASI shows ‘ASIR’, or ‘Air Speed Indicator Reading’.
Correct for instrument errors and you will get IAS, in other words what a perfect instrument would read.
I'd be interested to see a reference for that (other than wikipedia).
What you read on the dial is by definition the Indicated Airspeed, according to all the many texts where I have encountered a definition for it. It is what you see on the ASI, not what you get after reading the ASI and then applying instrument error correction (which would be some half corrected value between IAS and CAS).
‘Indicated airspeed’ means the speed of an aircraft as shown on its pitot static airspeed indicator.
Certification Standard Definitions - EASA
Indicated airspeed (IAS)—the direct instrument reading obtained from the ASI
FAA Pilot Handbook of Aeronautical Knowledge
The indicated airspeed (IAS) is the actual instrument indication for some given flight condition.
Aerodynamics for Naval Aviators
Indicated airspeed (IAS). The direct instrument reading
obtained from the airspeed indicator, uncorrected for
variations in atmospheric density, installation error, or
instrument error.
FAA Airplane Fllying Handbook
Indicated Airspeed (IAS)
IAS is shown on the dial of the instrument, uncorrected for
instrument or system errors
FAA Instrument Flying Handbook
[The] gauge is calibrated in knots of indicated airspeed (KIAS).
Naval Aviation Schools Command Fundamentals of Aerodynamics