Calendar and clock

Calendars

• An ordinary year has 365 days = 52 weeks + 1 odd day; a leap year has 2 odd days.
• A century year is a leap year only if divisible by 400 (2000 was, 1900 was not).
• The same date moves forward one weekday after an ordinary year, two after a leap year.

Clocks

• The minute hand moves 6° per minute; the hour hand moves 0.5° per minute.
• Angle between the hands = |30H − 5.5M| degrees.
• The hands coincide 11 times in 12 hours.