Thanks for the suggestion. They're not allowing anyone new to register.
I've found out pulling the thing in/out is how it's adjusted. Looks like pulled all the way out gets close to 0 and pushing all the way in is at its max.
Unfortunately, there are no numbers on it so you're left eyeballin' the arm float back away from the spindle when weight is set to zero and giving it the ol' college try and estimate it.