The normal desktop calculators seem counter-intuitive to me. Why emulate the limited interface (ie a numeric pad) of a pocket calculator, when you've got the power of a desktop computer and keyboard at your finger tips.
SuperKaramba Calculator is a very simple calculator theme, with a lot of hidden power. It uses the google calculator as its engine, which means that it can do complex calculations from a very simple interface. If the calculation is a simple mathematical expression, the theme will use the bc program, rather than going online. It does unit conversions and currency conversions as well.
You can enter an equation in mathematical notation, or in everyday language. For example:
four plus five
2000 kilometers per hour in feet per year
The theme stores the last 10 queries, so that you can go back over them.
The theme checks for invalid characters, and parentheses mismatches.
The theme also allows you to use the keyword "ans" in your query, which will substitute the last result into your current query. This could save typing a lot of text if you're chaining queries together.
How to use it ...
This is so simple to use, it doesn't really need a manual. The theme consists of three elements. A text entry box, a text display and a button.
To run a calculation, put your query in the text box. Then left click the button. The theme will go off and do its magic, and come back with an answer that will be displayed as text underneath the text box.
Sometimes what you enter may not be able to be processed, either because you've typed it wrong, or it doesn't understand you, or because you're asking it to do too much. If that is the case, then the theme will tell you.
To access previous queries, middle click on the button, and select the relevant query from the dropdown list.