Electrician and Mechanic, October, 1913, page 245:

Accuracy  of  Time  Signals
    Since the Arlington, Va., radio station has been sending out time signals at noon it has been noticed that these signals precede those sent out by the coast naval stations by a small fraction of a second. A large watch concern near Boston, Mass., recently made some tests to determine the actual difference between the Arlington signals and those from the Boston navy yard. The Boston signals, as were many of the coast stations, were found to be two-tenths of a second behind the Arlington signals. Since the Arlington signals are practically exact, the error in the signals of the coast naval stations becomes an absolute error, and not simply that between them and the Arlington signals.
    This error is due to the time lag of the successive relays between the transformer in the radio station and the observatory at Washington. When the coast naval stations used to send the time by hand as it came in on a telegraph sounder, this time lag of the signals was very apparent, because the hand is so much slower than the mechanical relay.