Perpetual calendar helper

Rules that protect a calendar movement

• Never use a corrector between about 9pm and 4am on the watch. Check the window.
• Never move the hands backwards on a perpetual calendar unless the manual says it's allowed.
• A perpetual calendar treats every fourth year as a leap year, so it will need one manual correction in 2100, which isn't one.
• An annual calendar needs one correction a year, on 1 March, because it can't tell February's length.