## Reverse polish calculator

### Completely free calculator with an in-built units converter which can be configured for more units by the user.

In the early 1970's, calculators were bulky and mostly unaffordable. By the mid 1970's, the price suddenly dropped to about half a weeks wages, so people began to
buy the things. There were two styles, Arithmetic and Reverse polish. Arithmetic calculators won the battle over the reverse polish, and nowadays most calculators
are arithmetic. The quickest way to tell what sort of calculator you are looking at is to see if it has an equals "=" button, only arithmetic calculators do so.
Reverse polish calculators have and enter button normally "ent" printed on the button instead, but does something different.

The advantage of reverse polish over arithmetic is in fact that you need less key strokes as reverse polish does not have brackets, you have to evaluate how to do
the calculation yourself.

Reverse polish is much more like how you would do simple calculations using a pen and paper. For example, if you had a pair of three digit numbers to add together,
say 123 and 234, you would not normally just write down the formula "123+234=" and just solve it in your head, this is how an arithmetic calculator works. You would
write down the number "123", then the number "234" underneath, then add them column at a time. This is how reverse polish works, you key in 123, then press enter,
then key in 234, then press the + button.

Similarly, if you had a more complex calculation like "(5x6)+(7x8)=" which is how you enter into an arithmetic calculator, 12 key presses, in reverse polish, you
evaluate the bracketed parts first. You would key in "5 ent 6 x 7 ent 8 x +", just 9 keypresses. The "ent" or "enter" key is like "write it down". So the keyed
sequence means write down 5, write down 6, multiply them, write down 7, write down 8, multiply them, add the two results.