A space for the serial number is left blank. The Great Britain patent number, 196,837, was first registered by J. Grassi of 49, Queen's Road, Finsbury Park, June 1 1922 and refers to an office coding device. The drums are sorted in a random order on the holder, then placed in the machine. Each quarter turn of a disc shows the alphabet in black with the vowels (including the letter Y) grouped in red and ending with a number so this can be set as a key, starting with a number order along one of the reading bars. Once an encription is decoded, a bar-slider is positioned across the start bar and the end result is read from the other side.