Indicated Mach versus True Mach Number
I need some help understanding Mach Number............
Is there a valid term 'true mach number', as opposed to 'indicated mach number' ?
As I understand it, Mach number is the ratio of true airspeed to the speed of sound..........Why would there be an indicated value of mach versus a true mach number.
Would it have something to do with the Ct (i.e. value of .8 or 1.0)of the temperature probe?
This question started with a query as to whether the mach value displayed in our cockpit (Honeywell Primus 2000 avionics suite) was a 'true mach number' or an 'indicated mach number'.
As for flying across the North Atlantic airspace, we are instructed to fly a constant mach number a.k.a. Mach Number Technique to maintain adequate spacing in trail of other aircraft. I have found reference material stating that this is to be a 'True Mach Number'
Thanks in advance