Equation of Time, Part II: Actual Watch Content. . .

[Jack Forster]

Hi everybody! So we have been having a MOST interesting discussion about the Equation of Time:

Click here to read the great community created Part I

. . .and what we have basically got so far is this:

1. Due to the eccentricity of the Earth's orbit (which causes the speed of the Earth's passage around the Sun to change over the course of a year) AND due to the tilt of the Earth's orbit from the vertical, there is an apparent change in the speed at which the Sun appears to move across the sky over the course of a year.

2. This phenomenon, which can be visualized in the analemma, means that the "sun time" and clock time will be different.

3. An effective intuitive way to express this is to say that the Equation of Time is the difference between the time told by a sundial, and the time told by a clock.



4. Furthermore, the Equation of Time complication, by itself, cannot be used to determine the actual time of solar culmination on any given day (that is, the time according to civil time when the sun is at it's zenith) because civil time is uniform across an entire time zone. It seems as if to determine the moment of solar culmination at noon, all you would have to do is add or subtract whatever the Equation for that day is from 12:00. HOWEVER, as several of you have figured out, this is only going to work if you are right on the line of longitude that determines the civil time for the timezone.

Now, there is much more to this story, which is as you may already have guessed really about a watch as well- the Jules Audemars Equation of Time:



As many of you may know this was the very first wristwatch ever to display the Equation of Time as a mechanical complication.

In addition, it also displays the correct sunrise and sunset times for the owner's predetermined location, and as well, it displays the actual time of solar culmination for the owner's location, regardless of whether he or she is actually located at the longitude line for the timezone from which civil time is derived. In addition it has an astronomical moonphase display.

In other words, every other EOT watch in the world keeps the EOT somewhat abstracted from an actual experience.

The Jules Audemars Equation of Time gives you the concrete ability to know the moment of solar culmination merely by observing your watch.

This is an interesting thing; as many of you know, civil time is a relatively new innovation. Prior to the development and use of time zones, every location on Earth simply had its own local time- and before clocks, that meant solar time. After the invention of clocks, of course, mean time became possible- as now you had a clock that ran at a steady rate throughout the year, instead of gaining and losing nearly a quarter of an hour, like a sundial.

Finally, with the development of civil time, it became convention to keep all clocks and watches set to a single time across an entire timezone. This was necessitated in many respects by the Industrial Revolution, and one of the main motivators of course was the development of railway networks. It is most difficult to coordinate the arrival and departure of trains if every blessed town on the line is keeping to mean local time!

Now, this gives us a bit of an answer as to the original utility of the Equation of Time- it allowed you to set your clock, and it allowed you to see if it was keeping time relative to a sundial. A sundial is never wrong. Depending on its construction you may at best be able to read the time to within a minute or so, but it's never going to start running fast or slow -except as determined by the Equation of Time. So, if it's the 18th century and you've just gotten a nice clock, you probably also get a sundial to go with it, and a printed chart of the Equation of Time, which lets you park the sundial in the yard, read off the solar time, and then set your clock to mean time by adding or subtracting from solar time whatever the equation is for that day.

What function does the Equation of Time have nowadays? Well, it remains a complication not only of great historical interest (and great rarity, there are very few equation watches made, even today) but also of great aesthetic appeal. However, the appeal of the Equation of Time is not to the novice collector, but rather to someone with a willingness to invest a little effort in understanding it, and also with a disposition to be moved emotionally by how the complication connects us to the cosmos.

Which is "reason" enough for me .

Now, the Jules Audemars Equation of Time has equation works driven off the perpetual calendar works. Here is a closeup of the JAEOT dial:



You can see the day of the week and calendar date indication at six o'clock.

Now, here is an "x-ray" view of the Equation works. Notice that the EOT hand is driven by a series of levers and gears which ultimately are moved by a gear attached to the pinion of the date hand:



You can see right away that the heart of the matter is the kidney shaped cam on which the nose of the first of the two levers that move the EOT hand itself rests. The shape of the EOT cam reflects the variation in solar time over the course of a year- essentially, it's that double sine wave we talked about, wrapped around to connect the endpoints:










And now, we can see how the whole thing works. (These illustrations, by the way, are all courtesy Audemars Piguet Le Brassus, and I think you will all agree they have done an incredible job illustrating the concepts and the mechanism.) The trick here, is that the cam has to turn very slowly- once a year- and the shape of the curve must be correct to within a very small tolerance as the levers amplify the shape of the curve to correspond to a display that covers half the arc of the outer dial!

Now, here is a riddle for you all:

We have said that the JAEOT is the ONLY EOT watch that can ALSO correctly show the correct time of solar culmination for the owner's specified location, regardless of longitude.

1. How does it do so? That is, how is the moment of solar culmination displayed?

2. What does this have to do with the fact that the half hour variation in the Equation of Time scale on the rehaut, corresponds exactly to half an hour on the dial? After all in most other EOT displays, you just have a hand showing plus or minus so many minutes in a separate sector on the dial. . .

Looking forward to your answers and thanks for hanging in there! I will give the game away a little ahead of time and say that this is one of my absolute favorite watches of all time. It may not have the immediate, obvious, muscular splendor of the Royal Oak Offshore (what does ) but it has a sophisticated, cerebral, and almost Platonic spiritual beauty which is virtually unmatched by any other watch. . .

Jack

[pj.m]

Cool report Jack- I especially liked the graphs and the cam overlays.

The watch can correctly show the culmination of the sun because the APEOT is actually made for each particular city. For example, New York owners would have a piece that says NY rather than Le Brassus. The watch is then set to that longitude and will work accordingly.
I cant remember exactly but I think the half hour differential is also located in different spots around the bezel for different cities, so when the watch reads the suns apex you will have the EOT reading. It would not actually be 12 noon but some other time, which the watch could tell better than I.

Thanks again Jack
Phil

[Jack Forster]

. . . there is actually plenty more; this is a watch with a LOT of depth to it conceptually speaking, and we have still to consider the sunrise/sunset complication as well as "unpack" how the JAEOT displays the correct moment of solar culmination. . . you are definitely barking up the right tree, by the way .

Jack

[pj.m]

My friend who just got this watch has yet to let me play with it. I think I am going to bug him for a while so I can try to get you guys some first hand info.

Phil

[rijowysock]

jack, thats amazing.. i always wondered what the internals looked like for some of these things...now i know.. im still curious to see what the internals for a 4 year perpetual look like compared to a 99 year perpetual tho.... would be something awesome to see

[take5]

Before reading this one, I didn't even know a watch like this one even existed It's fantastic to be able to read the time of sunrise and sunset of your watch dial!

I became so enthousiastic about the equation of time complication and this Jules Audemars that I ran to the shop today and bought one!

Just kidding, unfortunately this I will not be able to do... What I did do is find more info on the internet, which you have probably already found a long time ago since it's on AP's own website. There's a great set of movies explaining everything about the Jules Audemars EOT watch, from the concept of time and the equation of time, all the way to the workings of the sunrise and sunset complications and the perpetual calendar!

There are animated versions of the nice graphs you have put in this topic. It's all very, very cool! Especially the two location specific parts (almost like that EOT kidneything) that make the sunrise ans sunset time functions work properly for the location you're in

I hope I didn't kill the brainstorm session here, but I just couldn't resist to post this find.. Still, to explain such complications in words is a different thing than understanding their workings, so I'll pass on your latest questions and let the movies do the talking!

Here you go!
http://www.audemarspiguet.com/jp/nov...n_equation.swf

[take5]

After seeing these movies another question popped up.. How much will AP charge for recalibration of the watch for a new location?? I don't even wanna think about it

[Edgar]

Interesting! Great report.
Thanks a lot, Jack.

[harb]

Great report.
Beautiful watch - I'll have the silver dial one, please, Jack!

[pj.m]

take5- thanks for the link to the vids, very interesting. they fill in all of the missing gaps in info.
regards
phil

[Jack Forster]

Originally Posted by pj.m

My friend who just got this watch has yet to let me play with it. I think I am going to bug him for a while so I can try to get you guys some first hand info.

Phil

I am envious it would be very interesting indeed to hear your impressions.

Jack

[Jack Forster]

Originally Posted by rijowysock

jack, thats amazing.. i always wondered what the internals looked like for some of these things...now i know.. im still curious to see what the internals for a 4 year perpetual look like compared to a 99 year perpetual tho.... would be something awesome to see

. . . we have a LOT of photo resources from the various perpetuals we've covered, and as you may know the most recent issue is called "Perpetually Yours" and is all about perpetual calendars and astronomical complications. I'm sure we have some images we could use for comparison rattling around on the various huge numbers of computers our image resources live on, but it might take some digging to find them- my own image files in retrospect could be considerably more organized. Keeping them so is my New Year's work resolution . I'll see what I can do.

Also, bear in mind that these particular pics from AP for JAEOT are especially good and comprehensive; frankly they are MUCH better than many of the images I've gotten from other brands, both in clarity and in scope. I requested them from AP Le Brassus some time ago and was quite amazed- they have separate images for the base movement, the EOT train, the perpetual calendar works, AND the sunrise/sunset complication. I can't think of any other complicated watch I've written about where the brand has such well put together image and other explanatory resources.

Cheers,

JF

JF

[Jack Forster]

Originally Posted by pj.m

take5- thanks for the link to the vids, very interesting. they fill in all of the missing gaps in info.
regards
phil

. . . it takes a little digging to find them on the AP website (which to be honest does not, in terms of image size, ease of navigation, and general presentation, afford the best opportunity to appreciate many of the watches in their regular production series, I am forced to say. The areas of their website which present the special and limited editions are MUCH better but if you're surfing at 1600x1200 on a 19" color monitor like I am the images of the regular production watches are frustratingly small, and there's no way to look at higher res images.

If no one minds I would love to continue going through the other complications in the watch and finish up our little conversation on how to read solar culmination, as it's a fascinating subject and well, I just feel like it .

Jack

[Jack Forster]

Originally Posted by Edgar

Interesting! Great report.
Thanks a lot, Jack.

. . . more to come; the solar culmination, sunrise/sunset complication, perpetual train. . . it is intriguing though, isn't it, that the EOT complication is one of such depth? I just LOVE the EOT, it is my ALL time favorite complication. Well, and I love repeaters too, but with repeaters even more than most other watches, there is The Unpleasant Matter of the Bill .

Jack

[Jack Forster]

Originally Posted by harb

Great report.
Beautiful watch - I'll have the silver dial one, please, Jack!

. . I actually REALLY love the black dial and RG. Though I love that combo pretty much on anything .

Jack

[Quarks]

I learnt a lot from these posts. Thanks guys. I thoroughly enjoyed the topic. It has allowed me to gain a deeper appreciation for this complication.

[pj.m]

Originally Posted by Jack Forster

. . . more to come; the solar culmination, sunrise/sunset complication, perpetual train. . . it is intriguing though, isn't it, that the EOT complication is one of such depth? I just LOVE the EOT, it is my ALL time favorite complication. Well, and I love repeaters too, but with repeaters even more than most other watches, there is The Unpleasant Matter of the Bill .

Jack

The repeater is definitely my favorite complication, but I have to agree that they are slightly out of my price range. A good alternative is to buy a smaller pocket watch repeater that isn't very much and have it converted. A possibility.

Phil

[mf22433]

Originally Posted by Jack Forster

. . I actually REALLY love the black dial and RG. Though I love that combo pretty much on anything .
Jack

Jack, I agree with you, this combination is beautiful... and BTW many thanks for all these explanations, it is quite fascinating, I am definitely learning something.

Perhaps I have missed part of the explanation but I just noticed that these specific pictures shows the text "Le Brassus 12h35" and the half hour differential is precisely centered at 12h35... so I guess there is a reason?

Michel

[mf22433]

Originally Posted by mf22433

these specific pictures shows the text "Le Brassus 12h35" and the half hour differential is precisely centered at 12h35... so I guess there is a reason?
Michel

I just found another picture of this watch saying "Genève 12h36" so it is indeed related to the location...

Michel

[Jack Forster]

Originally Posted by mf22433

I just found another picture of this watch saying "Genève 12h36" so it is indeed related to the location...

Michel

. . . and a bit later today we'll pick up this thread- we've done the Equation of Time rather well I think, thanks to the community! -and we'll look at solar culmination next, but you have sniffed out the key point already; well done .

Jack