Indication of speed in computer, feeling less hot at first (4,6)

I believe the answer is:

mach number

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'indication of speed' is the definition.
'mach number' can be an answer for 'speed' (I've seen this before). I'm not sure about the 'indication of' bit.

'computer feeling less hot at first' is the wordplay.
'computer' becomes 'mac' (as in an Apple Mac).
'feeling less' becomes 'number' (I've seen this before).
'hot' becomes 'h' (abbreviation eg on taps).
'at first' says to put letters next to each other.
'number' put after 'h' is 'hnumber'.
'mac'+'hnumber'='MACH NUMBER'

'in' is the link.

Can you help me to learn more?

(Another definition for mach number that I've seen is " Speed".)

I've seen this clue in The Times.

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