When a watchmaker adjusts a watch movement to "a mean variation of ten seconds per month" just what does that mean? Is it with the watch in any 5 or 6 positions it stays with in ten seconds a month? or no more than ten seconds combined in any one position? what about heat & cold, isochronism?

Hi Harold,

Have a look at this: http://www.otws.co.za/files/Chronometers.pdf

The COSC doesn't conduct testing over a period as long as a month, so a statement that a watch is adjusted to "a mean variation of 10 seconds per month" is most likely a speculative number based on actual testing/adjusting over a shorter period and projected out to a 30 day average. Otherwise a watchmaker would need your watch for a very lengthy time.

Any testing for temperature variations are not really part of the "mean variation" vs. positional rates. Isochronism is another complete can of worms. COSC is recognized as pretty much the "standard" when it comes to chronometers, however, different watchmakers may choose to test in any way and establish a mean variation over some other time period. Some of this, of course, is related to the particular movement under test.

Regards,
Gene

Thanks Gene, The reason I asked is because of some research i'm doing on an 1867 SER. III Howard watch that belonged to Admiral Sigsbee, commander of the "Main" that sank in the Havana harbor in 1898, taking the watch down with it, the watch was quickly recovered and reconditioned to a mean variation of ten seconds a month. If I interpreted the information your linked website correctly, it would easily qualify with todays standards as a "chronometer grade" watch....
Harold

Harold,

Maybe it would qualify as a chronometer, and maybe not, but it may certainly depend on the perspective. Note that mean variation, by today's standards, is tested over a 10 day period, so using a 30 day mean 'could' mean that it did OK over 10 days. Also, we don't know about any temperature variation testing simply by using a mean variation result of 10 seconds per month. Keep in mind, however, that we're relating all this to COSC testing/certification. This is what the Swiss do today, but it's not etched in stone that the COSC methodology is the ultimate standard for determining chronometer status. It's just how 'they' do it. Also keep in mind that "it's always about the money". This most certainly applies to watches and clocks as well as everything that we deal with in a commercially oriented society...worldwide. Acquiring a COSC certificate interprets into more dollars in the watch market. Also, any standards from yesteryear are not necessarily the same as today's.

From my perspective, I'd have to simply conclude that any mechanical watch that's capable of staying within a 10 second mean variation per month from testing in 5 positions, and if it has some reasonable temperature compensation capabilities, is likely deserving of being classified as a chronometer, especially a watch from 1867 technology. Many of the Howards were/are extremely capable timepieces. A huge reason for this is directly related to the skills of some of the "finish" watchmakers that hand fitted, finished, rated, and adjusted these nice watches. This was obviously very time consuming and demanded close attention to detail. Given the fact that metallurgical technology was far from what it is today, it was quite an accomplishment for Howard to produce a fairly decent quantity of finished pieces to these standards. It took a lot of hard work and determination.

Gene