The most common and most likely answer to this crossword clue is the 12 letter word DIFFERENTIAL
I've seen this crossword clue in The Times
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Buddy explains!
The straight part
We know that "measure of variation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case measure of variation = differential.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 DIFFERENTIAL mean?
DIFFERENTIAL noun- The differential gear in an automobile etc
- A qualitative or quantitative difference between similar or comparable things
- An infinitesimal change in a variable, or the result of differentiation
- One of two coils of conducting wire so related to one another or to a magnet or armature common to both, that one coil produces polar action contrary to that of the other.
- A form of conductor used for dividing and distributing the current to a series of electric lamps so as to maintain equal action in all.
- Of, or relating to a difference
- Dependent on, or making a difference; distinctive
- Having differences in speed or direction of motion
- Of, or relating to differentiation, or the differential calculus