A 17-jewel movement is touted as a sign of a quality watch, but not many people know what this means. A watch mechanism is intricate, but needn't be complex.
"Jewel" isn't just a pretty-sounding name. Watchmakers use artificial rubies to prevent wear from friction. The 17 are arranged in eight pairs and an extra one called an impulse jewel. The impulse jewel tells the hands when to advance, and the others transmit this movement to the hands.
While 17 is as many as a watch really needs -- 21- and 23-jewel movements exist, and provide a small measure of extra protection, but it's not needed for most circumstances -- additional features with their own movements, such as perpetual calendars, have synthetic ruby bearings of their own.