Before there were clocks, sundials, or constellations, there were calendars, and as the earliest horological device, it enabled people to finally keep track of time. As luck would’ve had it, the concept of time however, isn’t as simple as 31 24-hour cycles per month and 365 days a year, which really complicates things when translated mechanically.

To counter the inconsistencies of time, watchmakers set about more advanced complications, of which their most prized result is the perpetual calendar. Armed with a mechanical memory that will enable the indication of the correct date for a century according to the Gregorian calendar, the perpetual calendar has the ability to take into the account leap years without requiring manual correction, with the only exception occurring when the secular year is divisible by 400. In simpler terms, the next adjustment required is in year 2100.

As one of the most classical complications ever created, the perpetual calendar tells a comprehensive tale of time, indicating not only the hours and minutes, but also the day, date, month, moon phase and leap year. Any other complication included is a bonus — and also a show off. Here are five that you should look into owning this year.