This is the Casiotron 79CS-53 Universal Calendar released by Casio in the late 1970s.
I introduced it before CASIOTRON CALENDAR 200 like this model, its selling point is the calendar display function.

CASIOTRON CALENDAR 200 has a system that allows you to determine leap years for about 200 years from 1901 to 2099 by inputting the remainder after dividing the Western calendar by 4 when setting the time.The days of the week had to be set individually, but this model has 60 years of calendars from 1970 to 2029 pre-registered, and has an automatic calendar specification that does not require setting the days of the week until 2029.
At that time, the lifespan of LCDs itself was said to be around 10 years, so it is surprising that they were designed to last for over 50 years.
In fact, this model is still going strong even after more than 45 years since its release.

This model's fatal flaw is that you can see the month and Sunday position on the calendar screen, but you cannot see the day, so you won't know what day of the week it is unless you display the date (= calendar display is actually unnecessary). CASIOTRON CALENDAR 200 is exactly the same.

When displaying the calendar, if you just flash today's date ("3" in the above example), you don't need two screens in the first place, right?
Since it is possible to hide the numbers 29-31 depending on the month, I would have liked to see something more done, but I guess it was technically impossible at the time.

Functionally, it is equipped with an alarm function and a stopwatch function.
The stopwatch function actually measures 1/10 seconds, and the photo on the top right shows "10 seconds 2" instead of "0 seconds 10."
It seems that measuring 1/100 seconds was technically impossible (or extremely expensive) at the time.

"Casiotron" is the name given to Casio's earliest digital wristwatches, but this model has "CASIO CASIOTRON" displayed on the back cover, and there is no display on the windshield.
Even on models from the same period, the display position of "CASIOTRON" varies considerably, and some models do not even have "CASIOTRON" displayed, so to be honest, I don't really understand the rules for how to use them.
There is another model of this model (UC-50W: UC seems to be an abbreviation for UNIVERSAL CALENDAR) that uses the same module, but that model does not have "CASIOTRON" displayed.
Also, as previously introduced CASIO F-100 was released before this model (79) in terms of module number (55), but "CASIOTRON" is nowhere to be found.
Does anyone know the display rules for "CASIOTRON"?