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About
to
go
off
perhaps,
indicating
right
(7)
About to go off perhaps, indicating right (7)
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0
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The whole clue is the definition (& lit or double definition).
How the clue works
Two meanings doing the work here, no wordplay to untangle. About to go off perhaps conjures a bomb that's TICKING away, while indicating right is what you're doing when you mark a tick next to something correct. Same word covers both ideas, which is why it's a double definition.