There is a WWII era 8 day Mercer Chronometer currently on EBay. It looks to be in pretty bad shape; however I am still looking at it. One curiosity I noticed, but have since verified on photos of other 8 day chronometers is that the “Wind” mark on the power reserve was on day 7, not--as I would have thought--between days 3 and 4.
I understand that the fusee design compensates for a weakening spring, but I still thought that 50% power reserve (as I see on most 56 hour models) was about optimal for accuracy. Would a sea captain really only wind a chronometer once a week when most recommended procedures and regulations say (I think) to wind them at the same time every day? Not counting zig-zagging during WWII, 7 days is a full Atlantic crossing on a single wind. Does anyone know how they were actually used viz-a-viz the more common 56 hour chronometer?
Posts: 88 | Location: Brunswick, Georgia in the USA | Registered: February 13, 2011
Having gone to sea commercially and using these items, I would have never had the standing orders to only wind these on the 3rd or 4th day, it would have been to wind each day at the same time and to log it into the offical log book as having been done. Just because it can go this long, doesn't mean that it should. Too much room to forget shipboard when you have an items which is to be done on every 3rd day (or some other variant). You have to make the process sailor-proof which brings us to simplicity.
As for the optimal power curve as the chain moves down the fusee, It's all a pretty similar gradient on an eight day movement, so the difference between every day and every 3rd is negligible. When you start getting down to the end of the wind, it is a more radical distribution.
I've noticed this as well on the markings for early Mercer's during the period. You'll also see a lot of them simply dont have the wind indicator on the dial, this was a Mercer thing.
Posts: 102 | Location: Houston, Texas in the USA | Registered: September 26, 2009
looks to me like it's just run down to day 7 out of 8,perfectly normal if you didn't wind it and it stopped at 7 or if it was still running on it's way down Now that isn't to say that some accuracy issues might not occur at a farther let down that would not so much affect the power curve in the mid-range
Posts: 1746 | Location: Aylmer, Ontario in Canada | Registered: December 15, 2009
Having been in the military, Michael's comments about routinizing the process makes sense to me, but then it begs the question, why bother to make an 8 day chronometer that tradition and exerience says you reset every 24 hours? Is there some other benefit derived from their design or use that justifies the presummed extra expense over a 56 hour variety?
Posts: 88 | Location: Brunswick, Georgia in the USA | Registered: February 13, 2011
After finding the listing, I'm also thinking that this is not original in terms of the movement. The balance wheel arrangement is not correct against any of the other 8 day Mercer chronometers that I've seen. It looks like it has been converted from a watch/clock at some time. It is very strange indeed.
Why bother with an eight day over a two day? Not sure of the rationale, when I sailed commercial ships I never once saw an eight day in service, they were all of the two day variety. The only experience I have with eight days is the ones in my collection. They are more scarce, that is for sure as well as having been more expensive. My guess on this is that it was perception that drove the eight days, in that it would be better to have a chronometer that ran longer. But as we know, that didn't play out well, as the rates were more variable on the eight days than the two days. If you look at the trial results from the observatory, you'll see very few eight day as having been entered with the trials. Couple this with the standard routine when shipboard (both commercial and military), there really wasn't a need for one that ran this long.
Don't get me wrong, they are neat, real neat. I've been trying to get a good one in my collection forever, which I've just finally done. So I'm glad that they made them......
Posts: 102 | Location: Houston, Texas in the USA | Registered: September 26, 2009
Interesting. Thanks for the insight. In an earlier discussion, you indicated you were on the hunt for an 8 day Kullberg chronometer, is that the one you finally found? Do you have any Photos you could share?
Posts: 88 | Location: Brunswick, Georgia in the USA | Registered: February 13, 2011
Now that isn't to say that some accuracy issues might not occur at a farther let down that would not so much affect the power curve in the mid-range 
