Sorry, NSF, but it is CTFQ (as in 'check'). Seen your typo?
Never need to know in that much detail except when I were an aeronautical student. Now-a-days I just reads the Mach meter and knows it gets lower as I gets higher - to the trop, of course.
Actually I flew with a co last week who
really wanted to know - only just had room for the blackboard and easel. I think he was impressed that the old git remembered (anything)