MK_,
associated with the answering cord as in Fig. 458. This increases the
normal potential to 30 volts. When the armature of the meter has made a
part of its stroke, it closes a contact which places its 40-ohm winding
in shunt with its 500-ohm winding, thus furnishing ample power for
turning the meter wheels.

[Illustration: Fig. 457. Western Electric Line Circuit and Service
Meter]

Such meters are in common use in large exchanges, notable examples being
the cities of New York and London. In London, there is a zone within
which the price per call is one penny and between which and other zones
the price is twopence. Calls within the zone either are completed by the
answering operator directly in the multiple before her or are trunked to
other offices in that zone. Calls for points outside of that zone are
trunked to other offices and in giving the order the operator finds that
the call circuit key lights a special signal lamp before her. This
reminds her that the call is at a twopence price, so in recording it she
presses the meter key twice. This counts two units on the meter and the
units are billed at a penny each.

In automatic systems it is not possible to operate a meter system in
which the operator will press a key for each call to be charged, because
there is no operator. In such systems--a notable example being the
measured-service automatic system in San Francisco--the meter registers
only upon the answering of the called subscriber. Calls for lines found
busy and calls which are not answered do not register. Calls for
long-distance recording operators, two-number ticket operators,
information, complaint, and other company departments are not
registered. In the Chinatown quarter of San Francisco, where most calls
begin and end in the neighborhood, service is sold at an unlimited flat
rate for neighborhood calls and at a message rate for other calls. The
meter system recognizes this condition and does not register calls
_from_ Chinese subscribers _for_ Chinese subscribers, though it does
register calls from Chinese subscribers to Caucasian subscribers. The
nature of the system is such as to enable it to discriminate as to
races, localities, or other peculiarities as may be desired.

[Illustration: Fig. 458. Western Electric Cord Circuit and Service Meter
Key]

In the manual meter circuits of Figs. 457 and 458, the meter windings
have no relation to the line conductors. In the automatic arrangement
just