There Are Pandas, and Then There Are Pandas.
And this isn't either of them! The Pandas we're talking about here, are watches, not bears. And what got me thinking about them (again) was a link posted this morning by @cm.rook who pointed a few of us to the very attractive (and not terribly priced) Yema "Rallygraph" Panda which, in it's most traditional arrangement, looks like the one on the left, but can also be had in the version on the right: The model on the left is a true Panda, while the model on the right is called a reverse Panda. The reason for that distinction is clear--Panda bears, only come in the first arrangement. Now at this point, everyone should be thinking about the most well-know Panda, The Rolex Panda, which is actually a Daytona, and among Rolex Daytonas, the most famous of which is the Paul Newman Daytona, which was famous first, because it was Paul's, and second because it sold at auction for $17.8 million (US Dollars). The story of that auction is well-known so I'll only...
Nov 8, 2019
https://www.ochsundjunior.swiss/watches/perpetual-calendar/videos/#Date-displays
The time is the time, and the four dots in a square are the year in the sense of relative position from leap year, with a red dot in the outermost position for leap years. But the whole year indicator rotates, and where it is at indicates the month. There are twelve months, so it just points at one to twelve o'clock and repurposes those indices for months.
Finally, the red dot on the outside perimeter is the day of the month. At first I thought, Oh, another German "approximate time" watch like the einzeiger, since who's going to memorize which dot is what date or who is going to count. But it turns out to be really simple: There are only six hour indices, 12, 2, 4, 6, 8, and 10. Not so uncommon. But 6 into 30 is 5. So all you have to do is look at where the red dot is relative to the hour indices. In the photo it's on the second index, 4 o'clock, so it's 2 times 5 equals the 10th of the month. You just have to be able to multiply by five and add or subtract one or two sometimes.
Apparently this approach cuts the mechanical complexity (and thus the reliability and cost) by an order of magnitude.
There is a customizer on the website where you can specify everything (different colors for hour hand and minute hand even), and from that I learned that there is also a seconds indicator and a power reserve. I'll leave that for homework.
I still haven't figured out the "control dot" at 1:30.