Just want to throw this in.
How it works:
If you pull the lever the tuning mechanism rotates. (about 25 degrees from what I can judge)
Thus loosening or adding more tension, going from E to D or D to E. With a quick flick of the lever.
In the picture: the upper plate with the tuning mechanism on it can rock back and forth, the plate where it's mounted on is fixed to the headstock.
I love these things. Almost all stuff I play is in DADG or EADG.