Compare simple date, annual calendar, and perpetual calendar logic with month-length and leap-year examples.
On 1 March after a leap year, a simple date watch may already be wrong if February was not corrected. An annual calendar usually needs a February correction. A perpetual calendar is designed to handle 28/29/30/31-day months automatically.
| Type | What it handles | Owner correction |
|---|---|---|
| Simple date | Usually assumes 31-day months | Often monthly |
| Annual calendar | 30- and 31-day months | Usually once a year (Feb) |
| Perpetual calendar | Month lengths + leap years | Rare under normal running |
A year is a leap year if divisible by 4, except century years must be divisible by 400.
Examples: 2024 yes · 1900 no · 2000 yes · 2100 no.
How do perpetual calendar watches work?They track month lengths and leap years so the date stays correct automatically under normal use.
What is the difference between annual and perpetual calendar?Annual usually needs a February correction; perpetual also handles leap years.
Do perpetual calendars need any adjustment?They need correct setting and care after long stops; designs vary on century handling.
Why are perpetual calendars expensive?Complex mechanism, adjustment, and servicing.