The NEW Evolution 20 is the next "Evolution" in the resistance activated releases.
The Evolution 20 no longer requires a spring change like the "plus" models with the ITS system.
One spring under a screw is the only adjustment needed with a weight range from 8 pounds all the way up to 40 pounds of holding weight. 
This new system also has the advange of a much more precise micro adjustment of weight, as well as improved consistency.