The Excess 3 code is a BCD code
in which the pseudotetrade comprises the first and the last three values of the 16 values of the BDC code. Due to the first pseudotetrade, the excess-3-code has an offset of 3 compared to the BCD-code.
3 in the BCD-code corresponds to the 0 in the excess-3-code, the digit 4 to the 1 and so on.decimal number "0" has the dual value 0011, the decimal number "1" has the dual value 0100, and so on. The Excess-3 code offers advantages in the addition of dual values because the tens carry is simulated.