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  http://blog.modernmechanix.com/2007/08/13/master-timekeepers-watch-clock-for-nation/

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    Master Timekeepers Watch Clock for Nation

    Above, granddaddy of all clocks in U. S. shows time in this
country and corresponding time in other parts of world

    Top, tuning radio at naval observatory to receive time signal from
naval radio station at Arlington.

    Center, reading tape from chronograph which checks synchronization
of clocks in thousands of a second

    Left, astronomer at naval observatory operating "Zenith tune,"
which checks master clocks. It photographs stars crossing the zenith.
Chronograph records time of stars' crossing.

    Above, master clock at observatory at exact noon, eastern standard
time, but its face shows seventeen o'clock, which is Greenwich time.
P. H. Tobleman points to mechanism that flashes long dash over radio
to give correct time


--
Margaret Stephanie Leber CCP, SCJP, SCWCD
 http://voicenet.com/~maggie
 AOPA 925383 - Amateur Radio Station K3XS - ARRL 39280 - AMSAT 32844
"The art of progress is to preserve order amid change
 and to preserve change amid order."-A.N.Whitehead