Nonhorological Complications
Sometimes various displays in or on a watch are counted as complications even if they have nothing to do with timetelling. Often-seen examples include thermometer, barometer (rare in watches; more frequent in clocks), compass, or altimeter. Many horologists will not count nonhorological complications when adding up the number of complications on a given watch or clock, and some purists even exclude the power reserve from the complications count because it does not show a time indication (although its function is related to timekeeping).
Read more about this topic: Complication (horology)