From Watches Wiki
Positioning of the second indication on the watch dial
It has to be discriminated between small seconds and central seconds.
Small seconds are to be found mostly at pocket watches or at manual winding wristwatches. This construction feature comes from the time when the wheels in the gear train of a watch were in a way that the second wheel was not in the center. If a second indication on the dial was desired, the stud of the second wheel was extended through the dial and a hand was attached. The position of the small second depends on the movement construction, but mostly it is located at 6 o'clock.