The term California dial is said to have been coined by dial maker Kirk Rich, who did dial restoration and refinishing in the 1970s and was located in Los Angeles. In short, the California dial is a combination of an Arabic and Roman dial, as can be seen in the images. This dial layout was at some point referred to as California dial because clients of Kirk Rich found it easier to use that name than talk about a combined Arabic and Roman numerals dial. The history of the California dial goes back a long time though, in a period when Rolex took care of the production of watches for Panerai. The first ‘Panerai’ watch with a California dial was their reference 3646. So the 2008 California dial Panerai Radiomir 1936 wasn’t the first but was inspired by reference 3646 that Rolex created for them.
