<Tr> <Td_colspan="3"> Also seen as 24 / 8, 2.5, 25 / 10 </Td> </Tr> <P> 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, 21⁄2 = HB, 3 = H, 4 = 2H . </P> <P> 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 . </P> <P> 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 of Austria - Hungary introduced their Koh - I - Noor brand, named after the famous diamond . It was intended to be the world's best and most expensive pencil, and at a time when most pencils were either painted in dark colours or not at all, the Koh - I - Noor was yellow . As well as simply being distinctive, the colour may have been inspired by the Austro - Hungarian flag; it was also suggestive of the Orient at a time when the best - quality graphite came from Siberia . Other companies then copied the yellow colour so that their pencils would be associated with this high - quality brand, and chose brand names with explicit Oriental references, such as Mikado (renamed Mirado) and Mongol . </P>

What type of wood are pencils made from