Er compressibility is corrected for 'initial' TAS in excess of 300KT on the CRP-5, it is true, but FAA docs say compressibility can be ignored below 200KT and 10,000ft. EASA questions seem to say 200KT and ignore the 10,000ft bit. It's a matter of judgement, at what point can a very small compressibility be ignored? How do you express what is essentially a mach number in terms of TAS/CAS/altitude? Is the FAA 200KT a CAS or a TAS? Depends on the reference material. The reference material isn't quoted of course, that would be too partisan.