Perfection grade scale?

[Marsim]

What is this used for and how do you use it?

 

[cannuck]

You put the bottom surface on a tilted (graded) surface, loosed the finger locknut, slide it back and fourth until the level bubble on top (broken in your case) is centered and the location of the lock nut indicates how many inches over 10' length is the "grade" (i.e. slope of the surface).

 

[Marsim]

Thank you for the quick response. Much appreciated.

 

[Firebrick43]

The 2 - 1/2" mark is the most important used point of the scale.