In the early 20th century, the U.S. inch was effectively defined as 25.4000508 mm (with a reference temperature of 68 degrees Fahrenheit) and the U.K. inch at 25.399977 mm (with a reference temperature of 62 degrees Fahrenheit). When Johansson started manufacturing gauge blocks in inch sizes in 1912, Johnanson's compromise was to manufacture gauge blocks with a nominal size of 25.4mm, with a reference temperature of 20 degrees Celsius, accurate to within a few parts per million of both official definitions. Because Johannson's blocks were so popular, his blocks became the "de facto" standard for manufacturers internationally, with other manufacturers of gauge blocks following Johannson's definition by producing blocks designed to be equivalent to his.