have the same hardness. Most manufacturers, and almost all in Europe, designate their pencils with the letters H (commonly interpreted as "hardness") to B (commonly "blackness"), as well as F (usually taken to mean "fineness", although F pencils are no more fine or more easily sharpened than any other grade. Also known as "firm" in Japan). The standard writing pencil is graded HB. This designation was in use at least as early as 1844. It used B for black and H for hard; a pencil's grade was described by a sequence or successive Hs or Bs such as BB and BBB for successively softer leads, and HH and HHH for successively harder ones. The Koh-i-Noor Hardtmuth pencil manufacturers claim to have first used the HB designations, with H standing for Hardtmuth, B for the company's location of Budějovice, and F for Franz Hardtmuth, who was responsible for technological improvements in pencil manufacture. As of 2021, a set of pencils ranging from a very soft, black-marking pencil to a very hard, light-marking pencil usually ranges from softest to hardest as follows: Koh-i-noor offers twenty grades from 10H to 8B for its 1500 series. Mitsubishi Pencil offers twenty-two grades from 10H to 10B for its Hi-uni range. Derwent produces twenty grades from 9H to 9B for its graphic pencils. Staedtler produces 24 from 10H to 12B for its Mars Lumograph pencils. Numbers as designation were first used by Conté and later by John Thoreau, father of Henry David Thoreau, in the 19th century. Although Conté/Thoreau's equivalence table is widely accepted, not all manufacturers follow it; for example, Faber-Castell uses a different equivalence table in its Grip 2001 pencils: 1 = 2B, 2 = B, 2½ = HB, 3 = H, 4 = 2H. Hardness test Graded pencils can be used for a rapid test that provides relative ratings for a series of coated panels but can't be used to compare the pencil hardness of different coatings. This test defines a "pencil hardness" of a coating as the grade of the hardest pencil that does not permanently mark the coating when pressed firmly against it at a 45 degree angle. For standardized measurements, there are Mohs hardness testing pencils on the market. External colour and shape The majority of pencils made in the US are painted yellow. According to Henry Petroski, this tradition began in 1890 when the L. & C. Hardtmuth Company