This is a SANYO DQ-C25P wristwatch with a calculation function.
DQ" seems to be an acronym for "Digital Quartz.
It seems to be a multifunctional digital wristwatch, but it has only an alarm function and no year and day of week display, stopwatch function, or light.

Moreover, even though this is a model from 1980s when wristwatches with calculation functions were still rare, it is cool that "CALCULATOR" is not displayed anywhere on the watch, but only "SANYO ALARM-QUARTZ" is written.
Well, it is obvious at a glance that it has a calculation function!

SANYO wristwatches are unique in the way they are listed by model number: this model is listed as "C25" on the back cover, "DQ-C25P" on the outer box, "DQ-C25 series" in the instruction manual, and "DQ752" as the module used in the instruction manual.
The disadvantage is that it is difficult to find information on the Internet, since there are only a few of them in circulation and they are described in different ways.
The SANYO amorton S517 introduced previously also has only the indication "S517" on the back cover, but the official model name and module used are not known at all.

It seems that SANYO also offers a model (model name unknown) with a function calculator function like the CASIO CFX-400, which looks almost the same as this model, so I would like to get one someday.