Although fake Rolex watches invented and registered the charming combination of Roman, Arabic, and when on the dial, I dare say the most closely associated with the California dial today is the popular Panerai. Rolex currently has no California dial in their current collection – you’ll have to look for vintage Rolex watches, while the fake Panerai offers several options. However, it’s worth noting that the 12-point luminous inverted triangle and the 6-point and 9-point baton index are now the standards for many Rolex sports watches, such as the submarine, the GMT Master II, and the Explorer II. 
Panerai has launched a handful of the best replica watches in recent years, which are all equipped with so-called “California dials.” Characterized by a mix of Roman numerals, Arabic numbers, and geometric shapes, this dial style was actually patented by Rolex in the early 1940s. Let’s discover more about the history of Panerai California dials and the Rolex connection.
In 1941, Rolex filed a patent for a very special dial design and was granted the patent on July 15, 1942. Of course, the patent document is written in French, but the first paragraph says that the patent was filed for the invention of a time dial with a time mark made up of Roman numerals and Arabic numerals. It goes on to say that the appendix contains four examples of dial-up inventions.
If you look at Fig.1 in the appendix, you will see that the top portion of the dial is home to Roman numerals while the bottom portion includes Arabic numerals. Accompanying these numerals are batons at 3, 6, and 9, together with the inverted triangle at 12 o’clock. The patent goes on to state that this special arrangement will give a clear view of the hours, will be easy to create with luminous materials, and will allow easy reading of the time – especially within wristwatch cases, where the dials are relatively small.
According to blogger and Rolex historian Jake Ehrlich, there are some theories out there as to why this dial design picked up the “California” nickname. The most common theory revolves around the Rolex Bubble Back craze of the 1980s when buyers were looking for pieces with this particular dial layout. It appears that dealers based in Los Angeles were selling significant quantities of them to satisfy the demand, further helped by a local dial refinisher named Kirk Rich, who produced numerous dials with this configuration. As a result, the “California Dial” name stuck.
Even though the Rolex replica never officially used the “California” moniker in reference to this style of dial, Panerai certainly has. The company frequently launched fake watches that are directly inspired by particular vintage models and equips them with what they officially call California dials. As some of you may already know, it was primarily Rolex that supplied watches to the replica Panerai in the mid-20th century with waterproof “Oyster” cushion-shaped cases and modified manual-would movements.