excess 3 code
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. The digit 3 in the BCD-code corresponds to 0 in the excess-3-code, the digit 4 to 1 and so on.
The Excess-3-Code is symmetrical but without the bit patterns 0000 and 1111. The dual numbers of the Excess-3-Code show this offset of 0011 for all dual values. Thus, the 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.