Comment 4 for bug 1226738

OK, I see two problems with this.

Firstly, the obvious one. If you do keep it behaving like this (despite no other calculator using this behaviour), then the output is wrong. Entering the above into the calculator actually displays the calculation as:

+ 9
- 0
= 72

Which is clearly wrong. If you're going to implicitly add numbers to the calculation, you need to actually display them.

Secondly, this behaviour makes little sense to me. I would expect that after entering an operand such as '+', if I then hit a different operand like 'x' it would change the operand, because I've just changed my mind. I would then expect '=' to work as an operand in the same way, thus removing any trailing operand because I've just changed my mind.

For comparison, entering the above into gnome-calculator gives a 'malformed expression' and into Android's calculator, gives 81.

It's probably worth getting some designer input on the second point.