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There are few pages online that describe this calculator made in Bulgaria. I like the 8-digit LED display. It can be powered from an external 6V DC source through a 3,5mm audio jack (!!).
Using a variable voltage power supply I could confirm that it works down to 4.5V and a small "L" appears in the leftmost position: this means I can use this calculator with USB power, without fully restoring the battery contacts.
Few keys are bouncy resulting in double-triple press, but I am not sure whether they were like that in the original, non-damaged calculator.
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This device is quite power hungry, because of the LED display, but modern batteries (or USB power) can handle it.