WatchUSeek Watch Forums banner
1 - 20 of 80 Posts

265 Posts
I have never liked very much the roman numbers on the dials. And, for that reason, I have never wanted to get a watch with the so-called California dial (with half arabic numerals, and half roman numerals).

But I have always wondered the reason why this combination. Several proposals circulate on the internet, but in very few works I have found a categorical reason for its origin. But you can find in many places why it has been called California dial (it was originally called "Error proof"), but I will talk about that later.

I decided to make a compilation of those investigations, and I think I have found the definitive answer to whether that mixed dial had any purpose other than purely aesthetic.

The german combat divers, the kampfschwimmer, were the first ones to use the Panerai watches with that "Error Proof" dial.

Let's explain the origin of this dial.

In this article, they give a lot of information about the California dial.

A brief history of the california dial

It was initially used by Rolex (since 1934, although it seems to be very marginal).

Here, one of these old Rolex, called bubbleback (for its protruding background, which housed the self-winding movement).

In that article there is no mention about the reason for that combination of numerals:

"The patent says that the thicker numbers made applying luminous paint easier, but nothing more about the reasoning for the two different numeral types."

Although later we will see that this statement is not true.

The first combat divers unit that existed was the Italian DECIMA MAS

Badge of the X Flottiglia MAS.

The watches of these divers were made by Rolex. This was requested by Panerai (who only made the dial). Rolex made all the original Panerai watches for the Royal Italian Navy from 1936 to 1956. The first watches were still wearing the Panerai brand on the dial, which were made with the traditional dial, only with arabic numerals. And with the characteristic sandwich dial, with a generous amount of dangerous radio, to make them visible in the dark.

It was not until 1944 that the so-called California dials were first put on the Panerai watches. But by then, Italy had already surrendered to the allies. Many members of the Italian army were forced to be taken prisoner or continue under the orders of the Germans. That happened with the X Flottiglia MAS combat divers, who trained the first german combat divers, the Kampfschwimmer. Panerai was already unable to manufacture the dials (which he first made in a plastic that the heat deformed, and then made them in aluminum), because he could not access that aluminum to make them (the Germans used it to make war material, more necessary), and asked Rolex to also provide the dials. Although the Germans had already completely appropriated all the material and machinery of the Panerai, the Swiss did not refuse to do so (so as not to get the Panerai family into trouble with the Germans). But to avoid problems themselves, they supplied them with unmarked dials. They are called anonymous dials (they did not want to identify that their material was used by the Germans). And among these, there were already those with the "error proof" format:

Here, one of these original combat watches.

About why Rolex made this dial, there are several theories circulating on the internet.

-One is something as simple and absurd as the dial with half roman numerals and half arabic is a dial sample, which was sent to a client, to choose which one he liked the most. The client left the dial as it was (maybe for laziness, maybe because he liked it that way). And then it became popular.

Another of these vintage Rolex.

- Another theory is more tactical: This dial was put in watches of combat divers (italian and german, although it was not its first destination, since -as we have seen before- Rolex put it in 1934). We must remember that those first diving watches were quite primitive, and that they did not have diving bezels.

One theory is that the dial with roman numerals in the upper part and arabic numerals in the lower one worked as an aid, to interpret what time it was in bad visibility conditions (the roman numerals would indicate the upper part of the watch). It seems obvious that, when wearing a watch on the wrist, the outside is the top, and that would not be necessary. But in poor visibility, breathing pure oxygen and in a stressful situation, any help is well received. What seems clear is that combat divers would not choose such a dial just for aesthetic reasons.

Perhaps avoiding confusions would refer more to what other divers could see, looking at their partner's watch, from a different position to the "natural" one.

A group of kampfschwimmer (you can see Panerai watches on the wrists of the divers at right), and three engraved backs (a common practice during WWII), one clean back, a view of the Cortebert caliber, and a front view of the watch.

Another of these original combat watches.

Initially, that dial was not called California (and, obviously, even less in Italy and Germany, during WWII).

The dial was called (during the 30s and 40s) "Error Proof" or "High Visibility dial". This already gives us an idea of why it was designed: for easy recognition.

Anyway, if the goal was to allow divers recognizing the top part of the watch, I do not think it was a good choice. Two different sets of numerical symbols just add visual confusion (something to be avoided underwater). In my opinion, a bold triangle on the top, with markers or arabic numerals around would have been a better option.

-There is another theory (that I have only seen in the justification given by Bamford -the custom brand of luxury watches- to present a version of its Rolex Submariner with California dial).

Bamford Watch Department Rolex California Dial Submariner

The California dial was originally designed for Allied forces, during World War II, and presents a combination of roman numerals and arabic numerals, intended to act as a "geographical shield" for troops that could be captured by the enemy. The mixture of styles should give the captive a degree of anonymity, since it was considered that a dial with arabic numerals indicated that the user was from the United States, where it was most frequent."

I do not give the above statement much credibility.

And there are also theories (as I said before) that this dial has no other motive than to do something different. And that Rolex did not do it for any functional reason. It was simply an art deco design, considered attractive in those years.

This is the original watch of the German divers (the Kampfschwimmer), from 1944

And this is the faithful recreation that Panerai did in 2006

Here you have a nice picture of that PAM 00249

Click this bar to view the original image of 940x500px.

A couple of pictures of German divers with those watches.

Click this bar to view the original image of 759x1024px.

These photos are from the following great article on these primitive Panerai (which does not explain too much about the functionality of this California dial).

The anonymous Panerai dials

And a movie (from 1944) where they show us how those kampfschwimmer made war, and where you see the precariousness of their equipment.

Engraved backs of these German watches

This is one of those early Rolex, with California dial.

And this is the California dial patent, which was presented by Rolex on 30th May 1941 (in the middle of World War II). It was published on 17h august 1942

Click this bar to view the original image of 1600x755px.

When I read in detail the Rolex patent on this dial, my doubts about "Why" it was made have vanished. And it is curious that I have not seen any references to this patent, when they want to explain the reasons for this special configuration.

This is what one of the patent's paragraphssays:

"It can be seen that this arrangement provides a clear and simple hour distribution, easy to make with luminous material, and that allows an easy time reading, especially in watches where the dials are relatively small.

On the other hand, the fact that the roman figures occupy half the dial and the arab figures the other half, clearly distinguishes the two halves ".

Another issue is that you agree with the reasons that Rolex states: that this distribution helps to interpret the time more easily. I do not see that it is much easier to see the time like this (although it is evident that it is clearly seen which is the top part of the dial).

The only explanation that has a bit of logic, in diving, is for divers who are not wearing the watch (who can look at their buddy from any position, and can be more prone to disorientation). The one who wears it on the wrist knows perfectly what is the top part (the one on the outside of his wrist), and I think that you should have a very strong narcosis (something that did not happen to those combat divers, who dived with pure oxygen, they did not go deeper than 10 meters, and had other problems than the narcosis in their dives) so that you get confused.

And we must not forget that those watches did not have any mark that indicated the time of diving, or bezel or anything like it (something that defines what a diving watch is, later).

Another theory, which involves combat divers, is that they asked for a watch with that kind of dial to be able to differentiate at a glance the nighttime hours from the daytime ones. Combat operations were carried out late in the evening and early at night, when allied naval targets were more vulnerable and divers were less visible. That's why this special dial: in roman numerals, at night (from 10 to 2), and in arabic numbers during the day (from 4 to 8). Obviously, in the second round of the dial, from 10 to 2 you are in broad daylight, but they dove in the other turn of the hands, at night.

Evidently, a fundamental characteristic that these watches should have was their ability to be seen in complete darkness. And for that reason they had a generous amount of radioactive Radio (hence the name of Radiomir). Obviously, these divers were not aware of how dangerous it was to wear these watches on their wrists for a long time. And let's bear in mind that the Radio may appear to have lost its luminosity in one of these old watches, but the material they carry remains perfectly active and dangerous (its half-life time is 1600 years!).

Here we can see a couple of photos of a radioactivity detector, which has been approached to a vintage Panerai. Even from behind (as the diver's wrist would receive it), the radioactivity is very high.

And when the dial is facing the detector, it triples.

This is one of the reasons why the owners of these vintage Panerai do not usually wear them very often.

Here we have one of these combat divers with his Panerai 3646. But, interestingly, he's not wearing a watch with California dial.

In fact, the first Panerai that used the California dial did not do so until 1944. This "Error Proof" dial was not installed until then. From 1940 to 1944, the Rolex 3646 was served to Panerai with the "normal" dial (with four arabic numerals). That's why most of the kampfschwimmer that you see in the photos carry watches with these dials.

And a curious detail is that the first batch of these "Error Proof" dials of 1944 came with a manufacturing detail. Rolex forgot to tell the manufacturer of the dials that the movement, despite using pocket watch movement Cortebert Cal. 618 (so it was a generous size and well visible, not usual in wristwatches of that time), it was going to be placed in a wristwatch. Therefore, the manufacturer made them so that the crown was placed at 12 o'clock, not at 3 o'clock.

Click this bar to view the original image of 970x550px.

To solve this unforeseen mistake quickly, Rolex made two small semicircles on the dial, at the height of 12 and 6, in which two small screws allowed to turn the dial 90º.

The second (and last) series of these dials "Error Proof" was already correctly oriented.

In this work they give many details about it:

And the author of this work (Jose Pereztroika), is also coauthor of this magnificent timeline of the Panerai, where you can see the evolution of these watches..

Click this bar to view the original image of 1600x907px.

Here you can see this photo in high resolution, to appreciate all the details.

Some more links that can expand your knowledge about these watches, and the combat divers.

The Rolex-panerai connection
Welcome to of Jake's Rolex World Magazine..Optimized for iPad and iPhone: Book Review: 100 Superlative Rolex Watches by John Goldberger [Part 2 of 4]

Panerai Mythbusters: Separating Fact From Fiction

The history of Panerai watches, at a glance

The Royal Italian Navy Frogmen Commandos: The First Professional Dive Watch In Action
Welcome to of Jake's Rolex World Magazine..Optimized for iPad and iPhone: Chapter 3: The Complete History Of The Rolex Submariner & SEA-DWELLER [Part 3 of 4]

And two impressive coffe table books, made by German researchers (Ralph Ehlers and Volker Wiegmann) about the history of these early Panerai.

In the second, they systematically analyse the 120 vintage Panerai specimens that -at the moment they made the book- were owned by collectors from all over the world.

It seems clear the motivation of this seemingly strange dial: To reinforce this theory of ease of reading.

A couple of advertisements back on those days, where it is emphasized that the dial is "proof-of-error" (by the digits differentiated).

Click this bar to view the original image of 627x875px.

The hands helped that clarity in distinguishing the hour.

There were also Tudor watches with that dial at that time.

After the WWII, the California dial disappeared. Apparently, it was reborn thanks to the interest of japanese fans, who wanted to invest in Rolex (after some economic changes in their country in the late 1980s, which left them with a lot of money to spend), and it seems that, in vintage watches (of small size) that they liked, they preferred that California dial. Rolex produced these dials for a very short time and -as indicated in the article on the first link- a dials manufacturer living in California (Kirk Rich Dial Corp.) specialized in them, and flooded the market. But when that economic bubble exploded, the California dials disappeared again.

Following that, this dial started to be known among watch enthusiasts with the nickname "California", although it has never had that name officially.

Until they were rescued by Panerai, in 2006, with the watch we have already shown: PAM00249

And another modern Panerai, with a California dial (and gold case).

Click this bar to view the original image of 1024x490px.

Not only Panerai has made watches with this dial. Glycine made an Incursore.

Fabre Leuva, a model with red dial (and an extra VI and XII in roman numerals).

Regia has also made one model with this dial.

And one of the most modern ones: this bronze Nethuns.

Dievas has a peculiarity. It has made California dials with the "official" configuration (roman numerals at the top).

But he has also done them with roman numerals on the left side (both with anonymous branding on the dial).

Click this bar to view the original image of 1024x1024px.

And Anonymous has done an even stranger thing: roman numbers on the left, and japanese kanji numerals on the right. The Anonymous Polluce Magnum.

Click this bar to view the original image of 1024x576px.

Well, I hope this post will serve to eliminate doubts about the reason of the California dial. Regardless of its origin, you may like it or not. To me, the combination still does not touch me. But understanding the reason for its origin has helped me appreciate it a little more.

Thanks for the patience in reading, and I apologise for my English mistakes.


304 Posts
Thanks for the write-up. I've always like California dials - they're certainly unusual, but in a way that appeals to me. I think Nomos makes the best-looking contemporary version with their Club line, which is a lot sleeker looking than the bulky Panerai cases.

6,136 Posts
Excellent write up! And thanks for your time and research! I've been wondering about this for a while! Also like you, I'm not drawn to this style of dial, but to now know the histories of it, gives me appreciation of it. Thanks again, Steve.

Sent from my K92 using Tapatalk

1,907 Posts
The first time I saw a California dial, I thought "WTF"? I had no idea that there was any history behind it, I just assumed it was a gimmicky idea someone had come up with. But the design has grown on me now.

3,869 Posts
Interesting article, thank you OP!

This diabolical Seiko was designed so if the enemy captured it (or ordered it from Jomashop), they wouldn't be able to see it, and would be vulnerable to capture while squinting hopelessly at the dial ...

The romans along the right side are clearly designed to baffle and confuse anyone attempting to coordinate an attack ...


Premium Member
9,529 Posts
Interesting. I have heard the practical usage theories, but I had never heard the prototype theory. Honestly, it sounds the most plausible in a way. This version sounds a bit Apocryphal, but the "practical" reasons sound like justifications after the fact, stretched as far as they can go. Very well put together post. Thanks.
  • Like
Reactions: boga and timefleas

2,077 Posts
And Anonymous has done an even stranger thing: roman numbers on the left, and some signs on the right. The Anonymous Polluce Magnum.

Thanks for the very in-depth and informative post.

Incidentally, the "signs" on the Anonimo Polluce Magnum are Chinese characters which are also used in Japanese kanji script.

1,640 Posts
Really interesting and amazing research. There is something really appealing about the simple Rolex California dials on an Explorer type watch. They should release a 3mm Explorer with California dial- I would buy it.
  • Like
Reactions: wemedge and boga

Premium Member
13,784 Posts
Very nice write up and thanks for sharing. My favorite watch with that type of dial would be a bubble back.
  • Like
Reactions: boga

1,658 Posts
Thanks for the interesting summary on your research.
  • Like
Reactions: boga

3,483 Posts
The first time I saw a California dial, I thought "WTF"? I had no idea that there was any history behind it, I just assumed it was a gimmicky idea someone had come up with. But the design has grown on me now.
Me too. I thought it was some dumb gimmick thing. I still think they are ugly, but now I respect it. As a retired military guy I appreciate the original military applications of this style.

Keep in mind, back in those days there wasn't a whole lot of research going on regarding military equipment. Mostly it was someone building something, selling it to the military, the military would issue it to the troops and if it worked, great. If not, then they loooked for something else (sometimes with fatal results). There wasn't much time time during WWII to fully research new technology. I think this dial was mostly a military experiment...and since it didn't catch on, it was probably ineffective as an "error proof" dial design.

Thanks, OP for the history lesson. Probably the most informative and interesting threads on this forum in a long time. Outstanding research.
1 - 20 of 80 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.