Bi-quinary coded decimal

Bi-quinary coded decimal is a numeral encoding scheme used in many abacuses and in some early computers, including the Colossus. The term bi-quinary indicates that the code comprises both a two-state ("bi") and a five-state ("quin"ary) component. The encoding resembles that used by many abacuses, with four beads indicating either 0 through 4 or 5 through 9 and another bead indicating which of those ranges.
Several human languages, most notably Khmer and Wolof, also use biquinary systems. For example, the Khmer word for 6, "pram muoy", literally means "five [plus] one". The numerals from 0 to 9 in Japanese Sign Language is based on bi-quinary, with the thumb acting as 5 units, and the rest of the fingers each standing for 1 unit. Roman numerals use a symbolic, rather than positional, bi-quinary base, even though Latin is completely decimal.
Examples.
Several different representations of bi-quinary coded decimal have been used by different machines. The two-state component is encoded as one or two bits, and the five-state component is encoded using three to five bits. Some examples are: