a common misperception, Marine Chronometers are not the perfect
timekeepers. What makes them so special is that they ARE nearly
perfect rate keepers.
What this means is that while a chronometer
is most unlikely to agree with standard signals sent from the US Naval
Observatory, it has the ability to maintain a very consistent
rate. In other words, its measurement (calibration) error is:
known, consistent, predictable, and (ideally) small.
illustration, many common clocks show the time to within a few seconds
over a week. Yet, within the week, the clock may be off by as much
as 15 minutes. There are a number of reasons for this, but it
boils down to quality of construction and attention to detail.
marine chronometer is constructed and used in such a way that its rate
does not swing so wildly over time. If it is .5 seconds per day
slow one day, it can be counted on to be .5 seconds slow per day a year
later. Equally important is that that .5 second loss will be
evenly divided across the the full 24 hours. The .5 second error
won't all occur just after it is wound, for example.
attention to detail is not surprising when you consider that ships (or
railroads) depended on precise timing for operations. For
navigators who are at sea for two to three years before being able to
check their chronometer against a known time signal, being able to
predict the error of the chronometer was extremely important. He
would multiply the known error by the the number of days at sea, and
adjust the dial reading accordingly to arrive at the time of day in Greenwich,
Marine chronometers are hung in gimbals for the
express purpose of keeping them in a "dial up" position.
This is not for the convenience of the navigator. When the
chronometer is dial up (or down), it is in a position that eliminates
errors due to the balance being out of balance (poise). By
eliminating the need to worry about poising errors, all of the maker's
efforts on the balance assembly could be directed to ensuring the
chronometer maintained a consistent rate across the wild extremes of
temperature encountered by a ship sailing from Maine to the Antarctic.
see, the adjustments made to correct the poise of the balance are the
same adjustments made to ensure stability across temperature.
These adjustments involve moving the position of weights around the rim
of the balance wheel. The adjuster has to decide which is the more
important goal: Temperature compensation (for marine chronometers hung
in gimbals) or Position Adjustment (for railroad watches kept at a
constant temperature in a pocket).
Since Railroad Watches are
worn in the pocket, and kept at constant temperature, the adjuster has
more freedom to worry about position adjusting. Which is a good
thing since the railroad worker is not likely to be sitting on one
Typical results I achieve:
- Marine Chronometers
Less than 1 second per day
Less than 2 seconds per day
- Precision Watches
Less than 1 second per day
- Other Deck Watches Less than 3 seconds per day
- Railroad Watches
Less than 30 seconds per week