For connecting receiving registers to the bus, we shall need a relay with 2 poles, one for the 2-line and one for the 1-line, for each register that can receive a number from the bus. For example, for entering the output register, we actually need only one 2-pole relay instead of the two 1-pole relays drawn for simplicity in Fig. 5. There will be 13 2-pole relays for this purpose, since only 13 registers receive numbers from the bus; registers _I_ and _C_5 do not receive numbers from the bus. We call these 13 relays the _entrance relays_ or _E relays_, since _E_ is the initial letter of the word entrance. [Illustration: FIG. 12. Select-Receiving-Register circuit.] The circuit for selecting and energizing the _E_ relays is shown in Fig. 12. We call this circuit the _Select-Receiving-Register_ circuit. For example, suppose that the _P_8 and _P_2 relays are energized. Then this circuit energizes the _E_10 relay. The _E_10 relay closes the contacts between the _C_1 relay coils and the bus; and so it connects the _C_1 register to receive the next number that is sent into the bus. This kind of circuit expresses a classification and is sometimes called a _pyramid circuit_ since it spreads out like a pyramid. A similar pyramid circuit is used to select the sending register. We shall need a relay for moving the input tape a step at a time. We shall call this relay the _MI relay_, for _m_oving _i_nput tape. We also need a relay for moving the program tape a step at a time. We shall call this relay the _MP relay_ for _m_oving _p_rogram tape. Here then is approximately the total number of relays required: RELAYS NAME NUMBER _I_, _S_, _C_, _O_ Input, Storage, Computer, Output 30 _P_ Program 4 _E_ Entrance 13 _MI_ Move Input Tape 1 _MP_ Move Program Tape 1 ———— Total 49 A few more relays may be needed to provide more contacts or poles. For example, a single _P_1 relay will probably not have enough poles to meet all the need for its contacts. [Illustration: FIG. 13. Latch relay.] Each cycle of the machine will be divided into 5 equal _time intervals_ or _times_ 1 to 5. The timing of the machine will be about as follows: