The most common and most likely answer to this crossword clue is the 7 letter word VERNIER
I've seen this crossword clue in Independent
V
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Buddy explains!

The straight part
We know that "Scale" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case scale = vernier.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VERNIER mean?
VERNIER noun- A secondary scale with finer graduations than the primary scale of a measuring device; the vernier measures between graduations of the larger scale.
- A secondary control input with finer control than the primary, or coarse, input; for example the vernier frequency tuning knob on a radio.
- A secondary system of force application for the attitude control of a spacecraft; for example a vernier thruster.