Scientist builds up from this small amount — aims at miscount being corrected (6,4,4)

I believe the answer is:

atomic mass unit

'scientist builds up from this small amount' is the definition.
(small unit of mass)

'aims at miscount being corrected' is the wordplay.
'being corrected' is an anagram indicator.
'aims'+'at'+'miscount'='aimsatmiscount'
'aimsatmiscount' is an anagram of 'ATOMIC MASS UNIT'.

I've seen this clue in The Times.

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