Returning now to the table we wish to make, we connect columns 30 to 36 of the punch card to Common. We connect column 79 of the punch card to the X Pickup. We connect the output No X to the males column of the table. We connect the output X to the females column of the table. In this way we make the number in the punch card appear in either one of two places in the table according to whether the number counts males or females. We might mention several more properties of selectors. A selector can be used in the reverse way, with X Pickup, X, and No X as inputs and Common as output (Fig. 15). What will come out of Common is (1) what goes into input No X if there is no X punch in the column to which input X Pickup is wired, and (2) what goes into input X if there is an X punch in the column to which input X Pickup is wired. In this case the logical equation for the selector is: _a_ = _bp_ + _c_(1 - _p_) Also, selectors can be used one after another, so that selecting based on 2 or 3 X punches can be made. [Illustration: FIG. 15. Selector.] 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. [Illustration: 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) Sequencer