A simple time-only watch is a masterpiece in its own right, but the pursuit of mechanical excellence led watchmakers to develop "complications"—functions that go beyond the simple display of hours, minutes, and seconds. These are the pinnacle of horological ambition.
The perpetual calendar is a mind-boggling feat of micro-engineering. A mechanism so intelligent it understands the varying lengths of months, even accounting for leap years, and will not require a manual adjustment until the year 2100 (a century-specific Gregorian calendar anomaly). The wearer is gifted with the illusion of a timepiece that understands the cosmos.