The most common and most likely answer to this crossword clue is the 12 letter word OSCILLOSCOPE
I've seen this crossword clue in The Guardian
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Buddy explains!
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 OSCILLOSCOPE mean?
OSCILLOSCOPE noun- An electronic measuring instrument that creates a visible two-dimensional graph, on a screen, of one or more continuously varying voltages or currents.