Completely off-brand, but interesting results

[DA74254]

Hello,
A couple of years ago, at a "school-start discount", I bought this calculator for €4 at the local supermarket in Riga, Latvia. Mostly because it was cheap, and it resembled my Casio FX-82 from my 9th year at primary school, back in 1983. The label states "1,5V AG13" battery, which I had to look up. It's LR44.
As the pictures shows, it has a "battery compartment", but you still have to dismount all 6 screws to open the back. Pictured, there are 2 pc LR44 (or "AG13"), so assuming they are in parallel.
Pictures showing the calculator in "off" state with the lid/cover including basic instructions, poorly placed as a paper sticker inside the cover. Though, see the pictue of the "calculator forensics" of the sin(cos(tan(atan(acos(asin(9)))))). It shows 8,999999998. That was a suprise for the very cheap and very Chinese clone. Even the Chinese Kinpo HP35s has less significant digits accuracy..