The 6-bit characters, in an encoding called CDC display code, could be used to store up to 10 characters in a word. They permitted a character set of 64 characters, which is enough for all upper case letters, digits, and some punctuation. It was certainly enough to write FORTRAN, or print financial or scientific reports. There were actually two variations of the CDC display code character sets in use — 64-character and 63-character. The 64-character set had the disadvantage that the ":" (colon) character would be ignored (interpreted as zero fill) if it were the last character in a word. A complementary variant, called 6/12 display code, was also used in the Kronos and NOS timesharing systems to allow full use of the ASCII character set in a manner somewhat compatible with older software.