In the language of logic, if p, q, r are the truth values of “there is an X punch in column i, j, k,” respectively, then by means of selectors we can get such a function as:
c = apq + b(1 - q)(1 - r)
Also, a selector may often be energized not only by an X punch but also by a punch 0, 1, 2, ···, 9 and 12. In this case, the selector is equipped with an additional input that can respond to any digit. This input is called the Digit Pickup.
Digit Selector
Something like an ordinary selector is another mechanism called a digit selector ([Fig. 16]). This has one input, Common, and 12 outputs, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12. This mechanism is often included in the tabulator and may be included in other punch-card machines. For example, suppose that we want to do something if and only if column 62 of a punch card contains a 3 or a 4 or a 9. Then we connect a brush that reads column 62 of the punch card to the Common input of the digit selector. And we connect out from the digit selector jointly from outputs 3, 4, and 9.
Fig. 16. Digit selector.
In the language of logic, if a is the digit going into Common, and if p is the impulse coming out of the digit selector, then the equation of the mechanism in this case is:
p = T(a = 3, 4, 9)