Old Premier understanding total after deductions (7)

I believe the answer is:

kennett

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'old premier understanding' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'total after deductions' is the wordplay.
'total' becomes 'ken' (I can't explain this - if you can you should give a lot more credence to this answer).
'after deductions' becomes 'nett' (I've seen this before).
'ken'+'nett'='KENNETT'

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

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