このコピーは原本と寸分違わず一致している。
This copy matches the original perfectly.
全く means 'completely' or 'entirely' and is a general adverb, whereas 寸分違わず specifically focuses on the absence of any difference.
Standard kanji spelling.
Variant with kana for 違わず; less common but still used.
From 寸 (すん, a very small unit of length) and 分 (ぶん, a fraction of a 寸), combined with 違わず (negative of 違う, 'to differ'), literally meaning 'not differing by even a 寸 or 分'.