The correct preposition here is 'by' as 'by' is used to convey the correct meaning. The other prepositions do not fit here. By here means according to and fits here appropriately.
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CCommunity
Some People Say: what is the time on ur watch is the correct answer.
But its not the correct answer:
Correct answer is: what is the time by ur watch.
Example: It is 10 O'clock by my watch.