Critical Dampening?

[ebncrdr]

I had the opportunity to run one of my shocks on a Roehrig Shock Dnyo a few days ago and was wondering if somebody could explain what critical dampening is exactly?

I also have my test graph with overlays of each run. I started at full soft then increased one click at a time. Which run is critical daming taking place and which run is dampening just before critical damping taking place?