For example,
60 seconds = 1 minute
60 minutes = 1 hour
24 hours = 1 day
7 day = 1 week
29-31 days = Month (approx.)
365/366 days = year
It's like for the imperial measurement of distance, where 1 mile = 5280 feet...
Edit: just to clarify, I'm more or less keen towards any consistent, decimal-based measurement systems like base-10 or base-12.
Calendar used in DPRK, basically normal gregorian but the dates are counted from 1912 as Juche era, in a combination of european system and partially Korean system.
Today date is: 19.08 Juche 112
Hmm, that's interesting...