My guess is different; these calculators did support negative numbers; I’d say: 4 –= 1 += gives: -3 4 –= 1 –= gives: -5 Manual for a similar model: https://w

My guess is different; these calculators did support negative numbers; I’d say: 4 –= 1 += gives: -3 4 –= 1 –= gives: -5 Manual for a similar model: https://www.oldcalculatormuseum.com/m-sharpqt8d.pdf https://www.oldcalculatormuseum.com/m-sharpqt8d.pdf