The IBM 1400 series are character-addressable machines, each location being six bits labeled "B, A, 8, 4, 2" and "1," plus an odd parity check bit ("C") and a word mark bit ("M"). For encoding digits "1" through "9", "B" and "A" are zero and the digit value represented by standard 4-bit BCD in bits "8" through "1". For most other characters bits "B" and "A" are derived simply from the "12", "11", and "0" "zone punches" in the punched card character code, and bits "8" through "1" from the "1" through "9" punches. A "12 zone" punch set both "B" and "A", an "11 zone" set "B", and a "0 zone" (a 0 punch combined with any others) set "A". Thus the letter A, which is "(12,1)" in the punched card format, is encoded "(B,A,1)". The currency symbol $, "(11,8,3)" in the punched card, was encoded in memory as "(B,8,2,1)". This allows the circuitry to convert between the punched card format and the internal storage format to be very simple with only a few special cases. One important special case is digit "0", represented by a lone "0" punch in the card, and "(8,2)" in core memory.