Bumpless transfer:

Bumpless transfer is the smooth transfer of a controller from one operating mode to another. The balance (BAL) position gives this smooth transfer while transferring the controller from the automatic to manual mode.  Within the BAL position, the controller is still in the automatic mode of operation, other than the deviation meter now denotes the difference among outputs of manual and automatic modes of control. A manual outcome is adjusted until the deviation meter displays no deflection. Now, the controller could be transferred smoothly from automatic to manual.

To ensure a bumpless transfer from manual to automatic, the manual outcome signal, denoted through the output meter, is adjusted to match the controlled variable value to setpoint. This will be denoted through no deflection of the deviation meter. At one it's matched, the M-A transfer switch could be switched from manual (MAN) to automatic (AUTO) control.