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Sizes of Watch Movements

Swiss and French watches are measured by the French ligne (line) which is one-twelfth of an inch of a Paris foot. One line equals .088814 of an English inch, or 2.25583 mm. The movements are spoken of as 14-line, 18-line, 19-line, etc. Mr. Aaron L. Dennison is said to be the inventor of the system employed for the sizing of American watches and he first applied it to the watches made by the American Horologe Company, about 1851. One inch was taken as a basing figure and to this 5/30 of an inch was added for a "fall" or drop, this being allowed so that the movement could be tipped into its place of seating in a ring or case; then every 1/30 of an inch formed a size. A 16-size would then be 1 inch + 5/30 + 16/30 = 1 21/30.