Why is there a number and a word on a pencil?

Numbers and letters on the sides of some pencils (Art & Drafting pencils) is used to signify the type of lead that it contains, or more specifically the hardness of that lead. The higher the number/letter combination, the harder the lead. Conversely, the lower the number/letter combination, the softer the lead. The typical pencil (#2 pencil) contains HB Grade lead. PencilPages.com notes (from The Pencil Hardness Test); "The hardest is a 9H, followed by 8H, 7H, 6H, 5H, 4H, 3H, 2H, and H. F is the middle of the hardness scale; then comes HB, B, 2B, 3B, 4B, 5B, 6B, 7B, 8B, and 9B, which is the softest. Another grading method uses numbers; the equivalents would be #1=B, #2=HB, #2-1/2=F, #3=H, and #4=2H." The H represents hardness and the B represents blackness.