SIGNED CHAS. FRODSHAM, 04650, AD.FMSZ, 84 STRAND, LONDON, STAMPED WITH LONDON DATE LETTER FOR 1873

Charles Frodsham (1810-1871) was a leading manufacturer of high-quality clocks, watches and chronometers and the last active member of a family that had played a prominent role in London clockmaking since the late 18th century. In 1840, he became a partner of John Roger Arnold who inherited his famous father's business.

At the Great Exhibition of 1851 in London, Frodsham exhibited a three quarter plate caliber signed with the letters "AD. FMSZ", a cryptogram for the year 1850. The code is formed by the numerical sequence of the letters in "Frodsham," with a "Z" for zero. The firm subsequently used the code for its most important timepieces.