Cool Vintage Find!

What vintage CPU is only 33 mm wide, 37 mm high, and 11 mm deep? Here's a hint, the QWERTY keyboard / terminal for it is only 14 cm by 5.5 cm. Well, I admit, its not an HP-01 (sigh...). But it is a Seiko Data-2000, complete with the pocket terminal-keyboard thingy, and in very good to excellent shape too. Little ware, and no scratches. The CPU / Watch battery was removed when it was stored many years ago, and I'm looking for any info on the battery type. The pocket terminal had a 2016 taped to the back, so I know that that takes. Actually, there is a real power switch on the terminal, I suspect the old battery is still good. Time for some web searches on this thing... As I recall, its got a whopping 4K. Does anyone here know the specific vintage of this thing?