Excess-3

Excess-3 or 3-Excess binary code (often abbreviated as XS-3 or X3) or Stibitz code (after George Stibitz) is a complementary binary-coded decimal code and numeral system. It is a biased representation. Excess-3 was used on some older computers as well as in cash registers and hand-held portable electronic calculators of the 1970s, among other uses.