Archived posting to the Leica Users Group, 2000/09/16
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi, I've been having fun reading all the threads lately. As a life long leica user, a sailor, and a navigator who has a half century old Hughes sextant and a century old Plath, and as someone who owns some mechanical watches, please allow me to make a comment about the meaning of the term "chronometer" in the context of navigation. To find my longitude at sea I need to know exactly what time it is both where I am located and in Greenwich, England. I can find the precise local time by using my sextant to determine when the sun is directly overhead. That, by definition, is noon at my location. To find out what time it is in Greenwich, I need a watch, or clock, set to GMT. The difference in time between these two locations translates into longitude. To make this process work I need to know the time quite accurately. Errors of a couple of seconds a day in time quickly accumulate into positional errors of miles over the course of a week. That may osund strange, but the reality is that the wronger you are the wronger you get. Here's where the counter-intuitive part comes along. To know GMT to a high level of precision, I don't need a watch which never gains or looses time. I need a watch which gains or looses exactly the same amount of time every day. I need to know it's error rate, and I need for its error rate to be constant. Once I know the error rate then it's only a matter of simple arithmetic to get GMT. Here's an example. If I know my chronometer gains a second a day, and I know that the time it showed was exactly right a week ago, then all I have to do is to subtract seven seconds from its reading and I have the exact time. A chronometer isn't a time piece which always shows the precise time. It is a clock with a known, constant error rate. It always gains or looses the same amount of time each day. What, as a Navigator, I can't tolerate, is a clock with a variable error rate. The sea is a very harsh environment. Harrison's struggle to make a chronometer wasn't to make one which always had the correct time on the dial, it was to make one whose error rate was unaffected by the humidity, salt, temprature changes, and constant aceleration and deceleration caused be going over waves. To make this relevant to Leicas, I never take my antique sextants, watches, or leicas out of the house! Barney John Coan wrote: > > Rolex makes a big deal about the "chronometer" certification, but anyone > who actually owns one will tell you that compared to today's cheap > quartz watches they aren't very accurate. At least mine isn't. Still, > they are a marvel of beauty and craftsmanship and salesmanship and hype > and certainly an icon. > >