This is the B630, a digital wristwatch released by CASIO in the 1980s.
In the 1980s, CASIO released a number of highly functional digital watches, such as the CFX-400, but they also released very simple watches like this model.
The B630's functions are limited to a seconds display in the lower right corner and the date when the upper right button is pressed; there is no backlight, no stopwatch function, no alarm function, no nothing.
In terms of functions, it is equivalent to the CASIO F-30, which I introduced as a “Cheapest CASIO,” and may be the original model of the “Cheap CASIO”.
(Though the latest Cheap CASIO have a built-in backlight, stopwatch, and alarm functions.)

This simple model must have been mass-produced at that time, but I can't find any information about it on the Internet.
Usually, if you search for the module number (632), you will find English manuals and other information, but I cannot find any information about this model at all.
Perhaps it was a model for JDM (Japanese domestic market).

Another feature of this model is the module inside.
At first glance, this module looks like the modules of today's very cheap Chinese digital wristwatches, but if you look at the back side, you will see the very same CASIO digital wristwatch module from the 1980s.
However, if you look more closely, you will see that the contact points with the buttons are not only on the “right side” where the buttons are attached, but also on the “top side” where there are no buttons!

Needless to say, digital wristwatches usually have operation buttons on the “left and right sides,” and occasionally there are models with buttons on the “front,” but the only digital wristwatch with buttons on the “upper side” that I can think of is the TAG HEUER Chronosplit Manhattan.
This model does not have a stopwatch function, and it is a mystery why this functionally “cheapest” model has a module designed so that the buttons can be operated on the upper side.

This model also has a similar (or successor) model called “B631".
The B631 appears to be identical to the B630, but uses a different module (module 634) that is slightly wider and has a different “PM” display position.
Module 634 is also designed to allow button operation on the upper side, even though its only function is to display the date.
Like the B630, the B631 is also a “phantom model” with no information at all.