The Clancy brothers were the crackerjack clean-up crew in the old Flatiron Building in New-York city.In appreciation for their punctuality the owners gave each of them a Callander watch.

Then the trouble began.While Brian's watch kept perfect time,Barry's watch lost a minute a day and Patrick's gained a minute a day.If the fellows set their watches to the correct time at noon the day they received them and never reset them after that, how many days would pass before the three watches would again all show the correct time at noon?
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For all three watches to show 12:00 again, one would need to wait the same number of days as there are minutes in twelve hours. This is 60 x 12 = 720 days.

One watch will have kept the correct time, one will have actually moved "forward" by twelve hours, and the other will have actually moved "back" by twelve hours.

If the watches are digital with "am" and "pm" on them, twice the time (1440 days) will be required.

I'm not even getting into it if the watches keep up with dates, days of the week, etc!

Excellent answer Coldfuse.