In reply to bpmclimb:
Cut'n'paste from my teaching handouts:
The plate locks when it is loaded, and to lower a second you need to rotate the plate to release the dead rope. Plates have a loop at the back to allow you to clip a krab or sling, to make this easier (beware - they’re often quite small and won’t accommodate chunky krabs at all).
For some plates, this is all the leverage you need - DMM’s Pivot releases quite easily. For others you need more force to rotate them - the best way is to attach a sling to the the back loop, direct this through another krab on your powerpoint, and clip it to your harness - so sitting back pulls on the sling and rotates the plate. If hanging, make this a foot loop and stand in it.
In all cases, the locking effect is removed very sharply and it’s quite easy to lose control of the dead rope. To remedy this, clip the dead rope into (another) krab on the powerpoint to redirect it. Then tie a French prusik around it and fasten the prusik to your harness belay loop. To lower the second, lean back (to weight the sling that rotates the plate) and slide the prusik simultaneously.
When setting this up, always put the French prusik on the dead rope before you set up the sling to release the plate; if you accidentally leant on the sling while tying the prusik you’ll drop your second!