Aside from expert ski terrain, the black diamond on the top scale starting at 19.2 inches is for truss layouts for 8-foot sheet goods—also referred to as the "black truss" markings. Originally the 19.2 was used in metric layouts. If you divide five into 96 inches (8 feet), it will give 19.2 inches—in other words, 5 trusses per sheet.
Count the black diamonds and notice that the fifth one lands on 8 feet. Since an 8-foot sheet spans half the distance of its size, then the second course would start at the halfway point (4 feet) or, in this case, at the third diamond, which is slightly over 3' 2 3/8". The 19.2 black truss marking is just a better span if you don't want to span 24 inches on center with today's undersized plywood.
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