The pencil hardness scale is commonly used to assess paint film hardness by checking what is the softest pencil that can mar the surface when you scratch it with a given force. In this case, we needed to assess whether exposure to a certain chemical degraded the integrity of the paint coating that we were counting on for corrosion protection.
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.
His link includes procedures, which suggest he was testing the hardness of some surface coating or similar:
> For the pencil hardness test, reference ASTM D3363, pencils of increasing hardness values are moved over the surface in a precisely defined way until one lead damages the surface. Surface Hardness is defined by the hardest pencil grade which just fails to damage the surface.
> Observe the pencil track. Sufficient pressure must have been applied either to cut or damage the coating or to crush the lead pencil point.
> If neither coating damage or pencil point crushing is observed, repeat the test until a definite observation is made.
> If scratching or damage of the surface occurs, proceed with the next softer pencil grade and repeat the testing process until a pencil lead grade is found which crushes and does not damage the coating.
> If crushing of the hardest lead should occur, the coating is therefore extremely hard and is beyond the measuring range of this test