Complications, in a mechanical watch, are mechanical disposals added to the basic movement, needed to indicate additional information to that of the hour. Complications are always connected to time flowing: to make some examples:
In this field, it is important to recognize also a complication that we usually consider as a basic feature of a watch: the central second hand.
The visual indication of the time flow, through the second hand placed in an off-centered subdial, should always be included in a watch, and cannot be considered as an additional complication (except in ultrathin models, where the second hand is eliminated so as to reduce the thickness of the movement).
However, when the second hand is placed in the centre of the dial, coaxial with the hour and minute hands, this can be defined as a complication: traditional mechanical of watches places in an off-centred position the second wheel, meaning that an additional wheel train is needed to transmit the movement to the centred second hand.