Unit of measure equal to 1/36 yard and since 1959 defined officially as 2.
54 cm (see metre ). David I of Scotland (с 1150) defined the inch as the breadth of a man's thumb at the base of the nail; usually the thumb breadths of three men
one small, one medium, and one large
were added and then divided by three. During the reign of England's Edward II , the inch was defined as "three grains of barley, dry and round, placed end to end lengthwise." At various times it has also been defined as the combined lengths of 12 poppy seeds. See also foot ; International System of Units ; measurement ; metric system .