It is three quarters of the way from the 3 inch mark towards the4 inch mark.Imperial rulers are normally marked in 16th of an inch with the4th and 12th marks slightly longer and the 8th even longer. The 4thmark is ¼, the 8th mark is ½ and the 12th mark is ¾; 3.75 inches is3¾ inches so on such a ruler it is the 12th mark to the right ofthe 3, and will be slightly longer than the 3 marks either side ofit.