The 2 out of 5 coding

Bell Labs developed during the half of last century a coding system dubbed “2 out of 5”.

The main idea was to reduce the ten wires used to represent digits 0-9 or just an improvement over bi-quinary coding that uses seven wires (two wires to indicate if it is higher or lower than 5 digit and five wires to represent a digit 0 to 4).

In the 2 out of 5 coding each wire represent one of these digits: 0, 1, 2, 4 or 7.

If you wants to indicate number 1 then wire 0 and wire 1 needs to be ON. If you wants to indicate number 3 wires 1 and 2 needs to be ON, and so on.

This is the complete sequence:
1 = 11000
2 = 10100
3 = 01100
4 = 10010
5 = 01010
6 = 00110
7 = 10001
8 = 01001
9 = 00101
10 = 00011

Did you notice 10 is wrong? (4 + 7 = 11), don’t worry, this is a special case used to represent the 0 digit.

Source: http://ibm-1401.info/qui-binary.html

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