This calculator was made by Mannics - and that's all it says. No name, no number, not even a 'made in Hong Kong'.
Revelations start coming thick and fast when we open up the battery compartment and read that this is 'MODEL 800' which tells us... nothing.
To learn more, we have to dig deeper. Some careful prying allows us to crack this bad boy open, which treats us to a view of the rather elegantly laid out insides of this device:
Beauty. Smells of the seventies. We have something to work with now: that NEC μPD941C chip drives the whole calculator and its date code translates to the 16th week of 1975 - but looking a bit more closely, it seems we could've also read that off the transformer labeled 'MANNICS': 7516, the sixteenth week of 1975. We have a date!
The device is 124mm long and tapers from 77mm wide at the bottom to 84mm wide at the top. It tapers from 28mm thick at the bottom to 29mm thick at the top. I think it used to be white, but tobacco and/or the sun had a thing or two to say about that. It turns on and off by a sliding switch to the bottom left of the screen helpfully marked ON.
It has a nine digit Vacuum Fluorescent Display (VFD), a type of display still used today in places that are subjected to abuse. You'll find them in cars, microwave ovens, and some handheld video games from the seventies. The technology includes phosphor anodes which can lose their potency over the years, fading the display. This screen's a bit faded, but still easily legible.
This device was a bit of a mystery, and it pops up here and there rebranded under the Prinztronic name, among others. Who was Mannics? You tell me, friend. I'll be waiting by my inbox.