euclid The Time Traveler's Clock, Руководство пользователя

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assured. Each instrument could be regulated to keep time within a second per day,
and—more important—its deviation from perfect time would be a very precise value
which would not change over the life of the chronometer. Each chronometer supplied
to the Navy (and, also, to the US Army Corps of Engineers) came with a record telling
when it was set to time as well as its measured error per day. From these data a
navigator could subtract the daily error multiplied by the number of days from the
currently displayed time, resulting in a very accurate “corrected” time for navigation.
Weaknesses of a mechanical chronometer include the need for continual winding; and,
if the instrument is allowed to run down, then all knowledge of time will be lost. Also,
while physically very robust, these instruments have to be handled with great care in
order not to upset the timekeeping. On larger ships the navigator kept two or three
chronometers for redundancy.
During normal operation, the TTC keeps the mechanical chronometer synchronized to
GNSS or atomic precision by means of a servo-mechanical system. It has been found
that a very small rotation of the chronometer every second will quickly cause the
chronometer to become synchronized to that rotation, because the escapement and
balance system in the chronometer become resonant with the applied mechanical
rotation. It is this resonance that affords the chronometer the ability to maintain
“perfect” time as long as the atomic or GNSS signals are present. If those signals are no
longer present, such as if all power is lost for an extended period, the chronometer will
revert to its natural rate. During normal operation, once per day, at midnight UTC, the
servo synchronization is turned off so that the natural rate of the chronometer can be
measured versus the atomic or GNSS standard, and that error is printed on a paper
tape.
Should the electronic clock systems in the TTC be lost, the user can use these historical
measurements to calculate the best time for navigation by applying the daily error to
the time read on the chronometer, as was done in the past, before satellite and atomic
standards.