> the calculator combined not only the functions [+=] and [-=], but also the multiply-divide functions [X -:-]. Very interesting. It finally solved the myster

> the calculator combined not only the functions [+=] and [-=], but also the multiply-divide functions [X -:-]. Very interesting. It finally solved the mystery for me. My aunt was an accountant and she had one of those in her office. I remember looking at the keyboard and wondering how in the world you're supposed to divide and multiply with a single button. [-=] seems to be something like "invert the previous operation and then produce the result"