thumb|upright=1.7|Cyclometer, devised in the mid-1930s by Rejewski to catalog the cyclic permutation|cycle structure of Enigma [[permutations. At top are the two rotor banks, one with lid open; below is the rheostat at left, and at right the array of lamps and switches labelled with corresponding letters.]] The cyclometer was a cryptologic device designed, "probably in 1934 or 1935," by Marian Rejewski of the Polish Cipher Bureau's German section (BS-4), to catalog the cycle structure of Enigma permutations, thereby facilitating the decryption of German Enigma ciphertext.