This read-write INTEGER is an action object: writing a stack unit number to it triggers a reset, or reboot, of that specific physical unit. An admin would use this to remotely recover a misbehaving stack member without having to power-cycle the entire stack or physically visit the unit. For example, if unit 3 in a stack becomes unresponsive to normal commands, the admin writes 3 to this object to remotely reboot just that unit while the rest of the stack keeps running.