NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Chronometers
From: Henry Halboth
Date: 2008 Mar 26, 13:24 -0700
From: Henry Halboth
Date: 2008 Mar 26, 13:24 -0700
Hi Alex, Congratulations on obtaining your new Chronometer. Generally speaking, the customary procedure was to keep an accurate record of the Chronometer Error (CE)by whatever means available to the navigator and to obtain from that record the daily rate, which was then applied to an observed time of observation in accordance with the formula you quote, adjusting the sign of total error application as necessary. I suppose there might be some argument with respect to methodology if the time between determination of errors was particularly great, such as might well be the case if Lunars or observations in a place of known Longitude or signal station time ball/flag be the method of error determination. In such latter cases it might not be proper to assume the rate to have been regular over the time interval, which, of course underscores to logic behind the importance of the predictability of a steady rate in a quality instrument. Since the advent of radio and radio time signals, it was customary to observe the CE daily at about the same time, which procedure, over a period of time reliably established a daily rate. I have a Hamilton USMC Chronometer, produced during WWII, or shortly thereafter, which I kept rated by daily radio time signals for many years and which consistently kept a daily rate of 1.5 seconds losing. From a practical point of view, it was customary to request a new chronometer be set slow so that the error be additive -I guess true sailors didn't subtract too well. It was also always considered appropriate to wind the chronometer daily at the same time, regardless of the actual run-down time and, on well run ships, to report that winding to the Master. The theory, right or wrong, was that the rate keeping ability was enhanced by using the same portion of the spring consistently. In my experience, at least, it was never considered appropriate to set a chronometer, and I have never seen a true chronometer that provided a setting mechanism other than by way of the center wheel stem which requires removal of the faceplate and use of the winding key via a special fitting on the arbor end. Hack watches, by comparison, usually had a setting mechanism associated with the winding stem. Again, according to my experience, chronometers were sent ashore for cleaning at reasonably frequent intervals and, at this time, were reset if the error had become unwieldy. They were also frequently rated while ashore, however, these shoreside rates seldom held up as sea.To allow a chronometer to run down was an unpardonable sin. The story of the US watchmaking industry, which had little experience in Chronometer manufacture, tooling up for such production at the onset of WWII is really remarkable, given the quality intruments produced. Good luck with the new toy. Regards, Henry --- alexwrote: > > Dear list members, > I think that of all (archeo)-navigation topics, > chronometers were not > discussed > on this list in all detail. > I recently purchased one (a late Soviet one), and I > have many > questions. > > 1. In the general books about chronometers (NOT the > navigation books) > they say that it is not important that a chronometer > shows "exact > time". > The important feature is the "constancy of rate". > For example, if a > chronometer > shows 24 hours and 1 second for each 24 hours > period, this is a good > chronometer, > because you can have an easy correction formula: > True time=(Chronometer time) minus (the number of > days since the last > checkong) seconds. > My question: what was the normal practice in XIX and > early XX century. > Did they routinely determine the daily rate and then > used a linear > correction formula > True time=(chronometer time) plus (the daily rate) > times (the number > of days since the last checking) plus constant? > > Or they just tried to regulate a chronometer to have > zero daily > deviation and then used > the time it shows as the true time? Somehow I cannot > find the answer > in the navigation manuals > and even in Chauvenet. > > 2. Since I bought my chronometer, I put it on test, > that is I wind it > regularly and check against > a good electronic watch. (The electronic watch I > check every month > against GMT on the internet). > The experiment (which is running for about 1 month > already) shows that > the chronometer is > slow by 1.4 seconds every day in the average, and if > I add this > correction, the chronometer > time is accurate within 1 second most of the time. > Is this a good > chronometer? > > The factory certificate says that the maximal daily > "going" has to be > at most 3.5 sec, and > this particular one showed 1.3 seconds on the > factory test. > > 3. There was a funny story of purchasing this > chronometer (from > Russia) which I can tell if there > is any interest:-) > > Alex. > > > > ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. 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