Book every anaesthetist will have? (7)

I believe the answer is:

numbers

'book' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for numbers that I've seen before include "Book of Bible; counts" , "Biblical book - anaesthetics" , "Figures, digits" , "Amounts; songs, etc" , "Fourth OT book - figures" .)

I've seen this clue in The Guardian.

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