I would like to obtain a further explanation by the moderator.
YOU ARE RIGHT, I have checked my AFM and there is a chart where you can convert Indicated Airspeed into True Mach number depending only on FL.
Anyhow I donīt understand the reason . For a certain FL (constant PA) and certain EAS ( IAS corrected by instrument and compressibility), I think ISA deviation will change density altitude and therefor TAS for the same EAS.
If OAT is higher there will be a higher TAS at same FL and EAS ( depends on relative density), when OAT increases speed of sound also increases ( depends on relative temperature). As far as decreasing ratio of temperature and density are not equal, How the relationship of airspeed to the speed of sound can remain constant?
Thanks again for your time.