the user as part of the key. Some of the links moved a 25-disk "key body" forward, some back. The A-21 (1923) and the A-22 (1925) consisted of a cylinder with 26 mixed alphabet strips around it. Another strip, bearing the normal A–Z alphabet was nearby, and could take one of two positions, dependent on the movement of chain similar to the A-1. In operation, the cylinder rotated one step, as did the chain, controlling the position of the reference alphabet. To encipher or decipher (the system was set up to be reciprocal), a letter could be read off from the reference alphabet to a cylinder alphabet using a slit at the top of the machine. Achievements and legacy Damm was an ingenious inventor and quick to adapt to new possibilities. In the 1910s and early 1920s no other cryptographic inventor had patents and working machines of such complexity and diversity. Damm was one among the four inventors of permutation wheels (the other three being Scherbius, Koch and Hebern). He was first with a number of innovations and ideas such as Storing a cryptographic key as a binary sequence, first as a chain of links, later on a pinwheel The use of an ”Influence letter”, an autokey function Cryptologic checksums to prevent illegal manipulation Superenciphering digital codes into pronouncable letter groups. This reduced the cost of telegraphy with up to 50% Designing electromechanical equivalents of delay shift registers and XOR gates. Damm´s strength lay in his ideas and clever constructions while his mechanical designs often were unreliable. And without high reliability it was hard to find customers. Despite having no cryptographic experience, Boris Hagelin managed to use the ideas of Damm´s B-13 to develop a crypto machine, B-21, which was to compete with Enigma for sales to the Swedish General Staff. In 1928 that order was secured. Boris Hagelin also participated in the development of a machine based on A-22, called A-34. There are no records about a serial production of the A-34. Inventions, production and sales The following cryptomachines were designed and built, based on Damm´s inventions. Patents The following patents concerning cryptography were issued to Damm in Sweden, with their United States counterparts: Swedish patent SE45343, filed 1915-07-20 — "Apparatus for Producing a Series of Signs", filed 1915-07-21.Implemented in A-1. Swedish patent SE52279 filed 19 19-10-10, — "Production of Ciphers", filed 1920-04-02. Implemented in B-1. Swedish patent SE57005,