How to checking abrasives discs planeness ?

How to checking abrasives discs planeness ?

The abrasives discs surface planeness is very important especially for the big size such like Chop Saw cutting disc - 10/12/14/16" inch.  If the disc surface planeness no good, the disc will easy out of shape and even cause big vibration during workings.

This video show how to checking it and you can see from the video - Blueshark Chop Saw cutting discs in good planeness condition.