Crossword Genius

Right this time one employs mathematical lengths in circles (8)

Ross

I believe the answer is:

radiuses

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'mathematical lengths in circles' is the definition.
I can't judge whether this defines the answer.

'right this time one employs' is the wordplay.
'right' becomes 'r' (abbreviation).
'this time' becomes 'AD' (AD, Anno Domini, as opposed to BC, Before Christ).
'one' becomes 'i' (Roman numeral).
'employs' becomes 'uses' ('use' can be a synonym of 'employ').
'r'+'ad'+'i'+'uses'='RADIUSES'

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