304,844. Standard Telephones & Cables, Ltd., Wright, E. P. G., and Wain, D. H. Oct. 31, 1927. Addition to 276.706. Automatic and semi-automatic exchange system.-In a multioffice system in which offices may be given two- or three-letter codes. the register-controllers comprise AB and C office registers, the former being connected to discriminating means to determine in accordance with the final setting thereof, whether the third digit shall be registered on the C office register or the thousands register. The first office digit is also sent to the thousands register to differentiate between a single impulse or the dialling of ' O ' for an operator, and code digits. The C register, if used, hunts under control of the setting of the AB register to determine which of them shall control the transmission of impulses, the other being released. The controller may be of the forward-impulsing or the revertive-control type. Specification 259,642 is referred to. Three digit code dialled. When the controller is seized, relays A, B energize, and the first digit is repeated to magnets VI, MR of the AB and thousands registers in parallel, relays C, DS being energized throughout. Magnet DDM of the distributing switch is now energized, over bank contacts MR2 (2 - - 9), stepping wiper DD2 to second contacts. Relay F energizes over DD2 and locks up, and release magnet MZ is energized to return the thousands register to normal. The next digit is repeated to magnet R1 Switch DD is again stepped when relay C restores, and the third digit is repeated to magnet V2. after which DD steps to its fourth contacts. Relay E now energizes [Q (not energizd), P (8, 9), E, R2,(5, 6), DD2 to earth], and completes a circuit for magnet R2., which interacts with relay E, so that the C digit switch wipers W4 hunt. If translation is to be effected from the AB switch, the contact on which wiper W3 (5) thereof is resting will be jumpered to the contact reached by W4 (6) after the first step, and relay P will operate [Q (not energized,), P (8, 9), W4. W3, P, F (6, 5), earth] and lock up. breaking the circuit of relay E to prevent further hunting. Magnet Z2 now returns the C register to normal and wipers W3 control translation. If translation was to be from the C register, hunting continues until contacts are reached, at which relay Q energizes over wipers W4 (6;, W3 (6), and locks up, shorting relay E to stop hunting. The AB register restores, and impulsing is controlled by wipers W4. Operation of relay P or Q earths lead SC to initiate routing. I Two digit code dialled. In this case, after two digits have been dialled, wiper W3 (5) is jumpered to contact TS15, so that relay P operates in series with relay Q which does not energize, and the distributing switch steps twice in succession. over F(14, 12), and P(17,18) in turn, and the third digit is registered on switch MR. Single impulse dialled. When relay C releases, magnet Z1 returns the AB switch to normal over the first contact of bank MR2, after which switch MR homes. Digit " 0 " dialled. When relay C releases, relay E energizes in series with relay Q, which does not operate, over wiper MR2, and the AB register steps to its first rotary contacts from earth at E (10, 9). Relay F energizes from earth at E (8, 7), and locks up, preventing further stepping of the AB register. Switch DD is now stepped to its second' contacts. Wiper W3 (5) is now resting on a contact jumpered to contact TS15, so that relay P energizes in series with relay Q which does not pull up, and translation takes place from wipers W3.