This read-only value reports how much of a specific stack unit's PoE power capacity remains unallocated, in milliwatts. An admin checks this per-unit free capacity before assigning new PoE devices to ports on that unit, since power isn't necessarily shared evenly or automatically across a stack. For example, if unit 2 shows only 2000 mWatts free while unit 1 has 100000 mWatts free, an admin would connect a new high-power camera to a port on unit 1 instead.