Difference between + key and += key

[Karl-Ludwig Butte]

Dear All,

I noticed that some early pocket calculator, like e.g. HP-10 (+= key only), Privileg Super 2002, Multiplus or some commercial desktop calculators, have a += key and a -= key, while most other machines have seperate +, - and = keys.

Does anybody know the functional and technical differences and the background reason why the alternatives += and -= keys were developed?

Thank you very much in advance.

Best regards

Karl

[Nigel (UK)]

This doesn’t fully answer your question, but it is a nice explanation of “adding machine logic”:

https://www.hpmuseum.org/hp10.htm

Nigel (UK)

[Thomas Klemm]

For details, see the examples in the HP-10 Owner's Handbook.

[Karl-Ludwig Butte]

Thank you a lot for your answers, Nigel and Thomas.

Best regards

Karl