The cyclometer was used to prepare a catalog of the length and number of cycles in the "characteristics" for all 17,576 positions of the rotors for a given sequence of rotors. Since there were six such possible sequences, the resulting "catalog of characteristics," or "card catalog,", when it was ready in 1937, comprised a total of (6) (17,576) = 105,456 entries. Preparation of the catalog, writes Rejewski, "was laborious and took over a year, but when it was ready... daily keys [could be obtained] within about fifteen minutes."
On November 1, 1937, however, the Germans changed the "reversing drum," or "reflector." This forced the Cipher Bureau to start over again and produce a new card catalog, "a task," writes Rejewski, "which consumed, on account of our greater experience, probably somewhat less than a year's time."
But then, on September 15, 1938, the Germans changed entirely the procedure for enciphering message keys, and as a result the card-catalog method became completely useless.
This spurred the invention of Rejewski's cryptologic bomba and Zygalski's perforated sheets.
United Kingdom Intellectual Property Office Publishes Application for Series of Two Trademarks to Moore Large & Co. for Multiple Products, Services
May 07, 2010; SOUTH WALES, United Kingdom, May 7 -- Moore Large & Co. Ltd., Derby, has filed the series of two trademarks "FORME, forme"...