ephone traffic day in the year.

[Illustration: WESTERN ELECTRIC MOTOR-GENERATOR CHARGING SET]

The daily variations in telephone traffic are closely related to
commercial activities and certain general features of this daily
variation are common to all telephone systems everywhere. Fig. 452 is a
typical graphic record of the traffic of a telephone exchange and
represents what happens in almost every town or city. The total calls in
this figure are not given as absolute units but would vary to adapt the
figure to a particular case. The figure shows principally that the
traffic in the night is light; that it rises to its maximum height
somewhere between 10 o'clock A.M. and noon; that though it is never as
high again during that day, the afternoon peak is over 80 per cent as
great; and that two minor peaks appear about the dinner hour and after
evening entertainments.

[Illustration: Fig. 452. Load Curve]

_Busy-Hour Ratio._ If the story told by Fig. 452 were to be turned into
a table of calls per hour, the busiest hour of the day would be found to
correspond to the highest portion of the figure, and in that busiest
hour of the day, if a number of selected days were to be compared, would
be found a very constant traffic. The number of calls made, or the
number of connections completed, in that particular hour, day by day,
would be found to be much the same. The ratio of the number of units in
that hour to the number of units in that entire day would be found to
be practically the same ratio day by day. This ratio of busy hour to
total day would be found to be much more nearly constant than the gross
number of calls per hour or per day.

In a large, busy city, about one-eighth of the total daily calls are in
some one hour; in a smaller, less active city, probably one-tenth are so
congested. This is reasonable when one remembers that in the larger city
the active business of the day begins later and ends earlier.

=Importance of Traffic Study.= A knowledge of the amount of traffic in
an exchange, and its distribution as to time and as to the divisions of
the exchange, is important for a number of reasons. Traffic knowledge is
essential in order that the equipment may be designed and placed in the
proper way and the total load distributed properly on that apparatus and
its operators.

For example, in an office equipped with a manual multiple switchboard,
the length of the switchboard is governed entirely by the number