divided into sections, each section being
about the width and height that will permit an ordinary operator to
reach conveniently all over its face. The usual width of a section
brought about by this limitation is from five and one-half to six feet.
Such a section affords room for three operators to sit side by side
before it. Now each line, instead of having a single jack as in the
simple switchboard, is provided with a number of jacks and one of these
is placed on each of the sections, so that each one of the operators may
have within her reach a jack for each line. It is from the fact that
each line has a multiplicity of jacks, that the term multiple
switchboard arises.

_Number of Sections._ Since there is a jack for each line on each
section of the switchboard, it follows that on each section there are as
many jacks as there are lines; that is, if the board were serving 5,000
lines there would be 5,000 jacks. Let us see now what it is that
determines the number of sections in a multiple switchboard. In the
final analysis, it is the amount of traffic that arises in the busiest
period of the day. Assume that in a particular office serving 5,000
lines, the subscribers call at such a very low rate that even at the
busiest time of the day only enough calls are made to keep, say, three
operators busy. In this case there would be no need for the multiple
switchboard, for a single section would suffice. The three operators
seated before that section would be able to answer and complete the
connections for all of the calls that arose. But subscribers do not call
at this exceedingly low rate. A great many more calls would arise on
5,000 lines during the busiest hour than could be handled by three
operators and, therefore, a great many more operators would be required.
Space has to be provided for these operators to work in, and as each
section accommodates three operators the total number of sections must
be at least equal to the total number of required operators divided by
three.

Let us assume, for instance, that each operator can handle 200 calls
during the busy hour. Assume further that during the busy hour the
average number of calls made by each subscriber is two. One hundred
subscribers would, therefore, originate 200 calls within this busy hour
and this would be just sufficient to keep one operator busy. Since one
operator can handle only the calls of one hundred subscribers during the
busy hour, it follows that as