The Poles intercepted many messages; they would need about 60 messages in the same daily key to determine the characteristic, but they may have many more. Early on, Rejewski had identified the six characters that made up the message key. If the code clerks were choosing random message keys, then one would not expect to see much correlation in the encrypted six characters. However, some code clerks were lazy. What if, out of a hundred messages, there were five messages from five different stations (meaning five different code clerks) that all used the same message key "PUUJJN"? That they all came up with the same key suggests they used a very simple or very common key. The Poles kept track of different stations and how those stations would choose message keys. Early on, clerks often used simple keys such as "AAA" or "BBB".