Nudge when maintaining one's balance (9)

I believe the answer is:

remainder

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'balance' is the definition.
(I know that balance can be written as remainder)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for remainder that I've seen before include "It's left over after division" , "deposit" , "Sell off book stock cheaply" , "The part that is left over" , "Leftovers" .)

I've seen this clue in The Guardian.

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