A tool for calculation in a lab, a customary instrument (6)

I believe the answer is:

abacus

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'a tool for calculation' is the definition.
I can't tell whether this definition defines the answer.

'in a lab a customary instrument' is the wordplay.
'in' indicates a hidden word.
'ABACUS' is hidden in the letters of 'lab a customary instrument'.

Can you help me to learn more?

(Other definitions for abacus that I've seen before include "Simple calculating device" , "calculator needed" , "What was counted on" , "one counts on it" , "Old calculator" .)

I've seen this clue in the Sydney Morning Herald.

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