A power reserve indicator is a complication on mechanical watches that tell the wearer how much power is left before the watch stops running. Mostly found today on automatic watches it is a sign of a watch manufacturer’s prowess.
But I would argue it is more logical that this complication be on manual wind watches instead.
Automatic watches wind themselves from the movement of your wrist, hence its name. A watch that is worn everyday will generally be still charged the next morning when you put on the watch, and thus be recharged.
Manual watches on the other hand will only be wound if the wearer does so. If he or she forgets to wind the watch for a couple of days the watch will stop running because of the lack of power and typical mechanical watch will have 40 hours of power reserve). Therefore daily wearers of automatic watches will not need to worry about power. So it does not make sense to have a power reserve on an automatic. Or at least it makes more sense to have a power reserve indicator on a manual watch.
So I scratch my head as to why watch makers do not marry the right complication with the watches’ functions.