Complication

A complication is any function of a watch beyond telling the hours, minutes, and seconds, such as a date, chronograph, second time zone, moonphase, or calendar.

Complications add interest, and often price, but they also add parts, which makes servicing more involved and costly. Complex complications can be expensive to repair if they've been neglected.

Test every complication when you take a watch in, and factor any faults, and the cost of fixing them, into your offer.

When a watch has several functions, list each one in your description; buyers searching for a specific complication often filter for it directly.