required in the business of the
telephone company, but also to supply a general clock and time-stamp
service to the patrons of the telephone company as a "by-product" of the
general telephone business.

Exchange service is measured in terms of conversations without much
regard to their length. The payment for the service may be made at the
time it is received, as in public stations and at telephones equipped
with coin prepayment devices; or the calls from a telephone may be
recorded and collection for them made at agreed intervals. In the
prepayment method the price per call is uniform. In the deferred payment
method the calls are recorded as they are made, their number summed up
at intervals, and the amount due determined by the price per call. The
price per call may vary with the number of calls sold. A large user may
have a lower rate per call than a small user.

=Local Service.= _Ticket Method._ Measured local service sometimes is
recorded by means of tickets, similarly to the described method of
charging long-distance calls, except that the time of day and the
duration of conversation are not so important. Where local ticketing is
practiced, it is usual to write on the ticket only the number of the
calling telephone and the date, and to pass into the records only those
tickets which represent actual conversations, keeping out tickets
representing calls for busy lines and calls which were not answered.

_Meter Method._ The requirements of speed in good local service are
opposed to the ticketing method. Where measured service is supplied to a
substantial proportion of the lines of a large exchange,
electro-mechanical service meters are attached to the lines. These
service meters register as a consequence of some act on the part of the
switchboard operator, or may be caused to register by the answering of
the called subscriber.

[Illustration: Fig. 456. Connection Meter]

In manual practice, meters of the type shown in Fig. 456 are associated
with the lines as in Fig. 457. The meters are mounted separately from
the switchboard, needing only to be connected to the test-strand of the
line by cabled wires. If desired, the meter may be mounted on racks in
quarters especially devoted to them, and the cases in which the racks
are mounted may be kept locked. In such an arrangement the meters are
read from time to time through the glass doors of the cases.

The meters are caused to operate by pressure on the meter key _