The first selector looks like the rounding selector, which the page I linked to has as UP . DOWN . 5 / 4-- Talk 13 : 33, 7 June 2011 ( UTC)
12.
If one of up to a hundred subscriber lines had the receiver lifted " off hook ", a linefinder connected the subscriber's line to a free first selector, which returned the subscriber a dial tone to show that it was ready to receive dialed digits.
