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NEAR-Fest Official News and Information => Mister Mike's "Mishigoss" Board => Military, Marine and Railroad Timepieces => Topic started by: W1RC on October 20, 2016, 08:15:56 AM

Title: Care and Handling of Marine Chronometers
Post by: W1RC on October 20, 2016, 08:15:56 AM
A marine chronometer should not gain or lose more than 2 seconds in any 24 hour period.

There is not a quick and easy way to set the rate on a chronometer, other than sending it to a specialist who is very familiar with how to do so (they will adjust the timing screws on the balance wheel which is extremely risky). 

Marine chronometers are not really meant to hold accurate absolute time, they are meant to have a steady known rate of gaining/losing time over various temperature ranges. On board ship, we'd know what the rate was and from that we'd be able to get time at Greenwich, which is very important in navigation. We never used it as a "clock" to tell local or absolute time. 

As for +/- 2 or 3 seconds per day, I'd be satisfied how it is working. Much more over that and I'd send it away for disassembly/cleaning/rating. 

Also, please be careful with this fine piece of machinery, don't ever touch/adjust the seconds hand, this will cause great damage to the escapement. If you do decide to change the hour/minutes, use the winding key on the hands and only turn clockwise. I'll make a suggestion, if you really want to use it as a clock, set the hours/minutes as described above, then every month make the adjustment to the correct time (which should only be a minute at that point, if it is 2 seconds out). 

Let's talk about winding. These are 56 hour chronometers, which means that they should run about 56 hours before they stop. Your best practice is to never let them run down and stop, this is hard on the mechanism. They should always be wound at the same time every day. Note that I did not indicate every other day or 48 hours. The reason for this is two-fold. One, if you wind each day, you'll be less likely to miss a day and if you do miss, it'll still be running. If you were on a 48 hour cycle, if you forgot/missed, then you'd have a chronometer that has completely run down, which is not good as described above. Secondly, when you let the mainspring run down 48 hours, the power applied on the mechanism is different than when the mainspring is fully wound. The fusee is supposed to even this power distribution out, but there are still some variations. It is best for the mechanism to keep the mainspring as close to fully wound as possible as the power curve is more consistent on a fully/nearly fully wound mainspring. 

If you do decide that winding this thing is too much, you should wind it all the way up and then cork the balance wheel, this will prevent the chronometer from running and will provide a constant pressure on the movement, which will be good for all the parts involved. 

Winding these does get tiresome, it drives my wife crazy when I have my eleven all wound up and ticking every half second...... And since I travel, I normally keep them corked and wound and only let them truly run when I know that I'm going to be available to wind daily and have the time to re-cork at the end of my "chronometer play time.