Download Mini Calculator
Mini Calculator is a very small and portable tool to be used everywhere and every time you need it.
Even when it looks very Windows Built-in calculator like, it's not the same.
This one comes with a lot more of features that will let you customize your calculator according to what you need.
It's totally free but don't let that fool you, this application focuses more on functionality than on appearance.
It will resolve any complex equation you request. When you first install it you will see that is quite small but if you select the advance mode function it will double its size, and of course, its features.