The tourbillon system was made to compensate the Earth’s gravitational force by mounting the escapement in a revolving cage. It gives the watch a better accuracy. This complication is known as one of the most difficult to make.
The power reserve indicator tells you the time the watch will continue to function. It can either be seen on hand winding or automatic watches.
Watches featuring a small seconds have a smaller subcounter, usually located at 6h, which indicates seconds.