Terminated: unknown
This calculator is dual powered, there’s a solar cell as well as a battery. When the battery runs out it is very hard to open the case. There’s one screw at the bottom and when unscrewed one needs to apply quite a lot of pressure to open the case, especially since the case is glued to the black cover.
This calculator displays negative numbers using the text "MINUS -" at the top left of the display. Errors are indicated by an "ERROR" sign at the top right of the display. When there’s a non-zero number in the calculator’s memory it displays "MEMORY".
There’s also a "GPM"-key but I haven’t yet figured out what it does... "GPM" might stand for Graduated Payment Mortgage.
Many thanks to Susan Waucomont for donating this calculator!