Max is the manufacturer listed max and min expansion range. When you select this, I'll also show you lines indicating where 10% and 60% expansion range is. Many people consider 10% and 60% expansion to be a reasonable usable range for cams, but these numbers may differ from cam to cam and also depend on your risk tolerance.

Usable is 10% to 60% of the max range, unless a manufacturer publishes a different number. Metolius is currently the only manufacturer that publishes a usable range. When you select this option, the entire bar represents the usable range.