This is the difference with complicated timepieces.
The clock is one of the oldest human inventions, meeting the need to consistently measure intervals of time shorter than the natural units: the day, the lunar month, and the year.
A watch complication is any function that exists in addition to telling time (displaying hours, minutes and seconds) on a timepiece.
These watch complications enable special functions that are performed and displayed on the watch to enhance or simplify your life.
The combination of several hundred tiny gears, jewels and springs enables the timepiece to complete incredible functions; functions that are assembled by hand and not completed by a computer chip.
In horology, a complication refers to any feature in a mechanical timepiece beyond the simple display of hours and minutes.