Banking Error
When by a sudden circular motion of the watch in the plane of the balance (a very frequent occurrence when wearing the watch, or winding it up in a careless way), the vibration increases to more than two full turns, the impulse-pin strikes against the outside of the fork, which cannot yield, because it is leaning against the banking-pin or edge. By the violence of this percussion there is some danger of injury, not only to the ruby-pin, but also to the balance-pivots, which are often bent or broken by the reaction. But more than that, all such cases are accompanied by a considerable acceleration of the rate of the watch, producing under unfavorable circumstances great differences in its time-keeping.