Terminated: unknown
There’s no display indicator to show that there’s a non-zero number in the calculator’s memory. The Σ+ key simply adds to the memory and is equivalent to what would normally be called an M+ key.
There are other display indicators however. When the arc key is pressed (for the reverse trigonometric functions), this is indicated by the lighting up of the rightmost decimal point. When the calculator is in RAD-modus (switched using the R/D key) this is indicated using the leftmost decimal point. An error is indicated by a mirrored "7" in the leftmost display segment.
This calculator has a power-save mode, after a timeout the display changes to one single dot to preserve power.
The calculator as a built-in battery which I have removed from this one because they were leaking acid. They are three AA size batteries and could probably be replaced by two modern NiMH batteries.
This calculator’s keys are not so good and tend to bounce a lot.