A more common design, shown in the first picture above, allows the position of the third brush relative to the main brushes on the dynamo to be adjusted. Initially fixed at time of manufacture, it can subsequently be changed at servicing or overhaul time if required after which it remains fixed until the next service. By moving the position of the field brush, the voltage applied to the field coil can be varied, with consequent increase or decrease of charge rates. To increase the charge rate, move the field brush in the same direction as the rotation of the armature. To decrease, move the brush against the direction of rotation. This is an improvement on the previous design but, once adjusted, still gives only one fixed charging rate.