Talk:Wheel train

Going train arrangements
Depending on the position of the 4th wheel with respect to the rest of the going train different going train arrangements can be defined - small seconds, indirect center seconds, direct center seconds and coaxial direct center seconds.

In the traditional small seconds going train the 4th wheel is located at 6 or 9 o'clock position, and it carries the small seconds hand on its extended pinion. In contemporary direct center seconds going trains the 4th wheel is found at the center of the movement, where, historically, the second wheel was located. Most often the minute wheel (now called second or intermediate wheel) is located off-center and it drives the minute hand by an intermediate wheel that is out of the power flow. In an alternative arrangement both the minute and the 4th wheel are coaxial in the center, and the seconds hand is driven by the 4th wheel arbor which penetrates the hollow cylinder of the minute wheel, a coaxial direct center seconds going train.

Historically, an indirect center seconds arrangement needs to be mentioned - the minute wheel is still at the center and the 4th wheel is its traditional location at 6 or 9 o'clock, but the seconds hand is at the center and is driven by an intermediate wheel which is out of the power flow.