You use the kit to test the harness of a finish coating, like a paint or a ceramic coating for cars. Pencils have their own hardness scale which can be used to gauge the hardness of the coating. Its really more of a relative qualitative test than quantitative as you'd use this for sample/coupon testing identical coatings. There are more absolute, quantitative methods to measure various hardness characteristics (scratch, indentation, and rebound). Like you'd use the pencil kit on a factory floor to make sure each paint sample performs the same, the sample being a small area on the product or a plate that's painted the same way.