It's a ... what is it?

I've had this for ages and can't even remember where it came from. It comes in a cardboard pocket which you see here:





And slides out the side.

It opens like a little notebook to reveal...

This very fascinating face.


A stylus sits in a side pocket.


And is used in these slots.

Like here where I started where the 5 is and pushed down. And now 5 shows up at the top row.


To clear all the numbers this bar slides up.


And this is printed on the side.

It seems quite simple...and yet I can't figure out how to make it work as an "adding machine." Of course I'm rubbish at anything even remotely mathematically related so that could explain a lot...

But it's kinda neat, right? I like it anyway.