AES/newspost wrote:

Listening to audio channel 9 on United, at higher altitudes and during
cruise I hear ATC say things like "What's your mach?" and "Maintain
mach 77" and at lower altitudes and during approaches "slow to 180" or
"maintain 250 for spacing".

I appreciate that these are occurring in quite different ranges of
operation and the units involved are very different in scale, but I'm
still curious about the potential confusion, or at least possibility for
same, in using two different sets of units for the same quantity

I don't think a UA pilot is going to confuse 250 knots with 2.5 Mach or
180 Mach any more then he will confuse mach 77 (.77) with 77 knots.