Book of use to the anaesthetist? (7)

I believe the answer is:

numbers

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'book' is the definition.
(book of the Bible)

I cannot understand how the remainder of the clue works.

(Other definitions for numbers that I've seen before include "Amounts; counts" , "Principal features of mathematics" , "They subdue the pain" , "quantity" , "OT Book 4" .)

I've seen this clue in The Irish News.

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