The tower grain was the finest unit of the British tower system of mass/weight, intended to represent the weight of a grain of wheat. It had the value of 45/64 of a troy grain (0.703125 troy grain) by definition, or 1/7680 of a tower pound. (Thus, reversing the definition, 1.42222222 tower grains = 64/45 tower grains = 1 troy grain.)