The encrypted doubled key was a huge cryptographic mistake because it allowed cryptanalysts to know two encipherments of the same letter, three places apart, for each of the three letters. The Polish codebreakers exploited this mistake in many ways. Marian Rejewski used the doubled key and some known daily keys obtained by a spy, to determine the wiring of the three rotors and the reflector. In addition, code clerks often did not choose secure random keys, but instead chose weak keys such as "AAA", "ABC", and "SSS". The Poles later used the doubled weak keys to find the unknown daily keys. The grill method was an early exploitation of the doubled key to recover part of the daily settings. The cyclometer and the "bomba kryptologiczna" were later exploitations of the doubled key.