Ability to calculate shower pressure in boudoir (10)

I believe the answer is:

brainpower

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'ability' is the definition.
(brainpower is a kind of ability)

'shower pressure in boudoir' is the wordplay.
'shower' becomes 'rain' (rainfall).
'pressure' becomes 'p' (abbreviation).
'in' means one lot of letters goes inside another.
'boudoir' becomes 'bower'.
'rain'+'p'='rainp'
'rainp' placed into 'bower' is 'BRAINPOWER'.

'to calculate' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Another definition for brainpower that I've seen is " intelligence".)

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