Calculators
 

If you could have access to any calculators (torque, displacement, etc) that you would require on a (semi)regular basis, what would they be? Start with the easiest and most commonly desired, get harder from there. If you have access to formulas (not pre-built calcs), include them.

I am working on application development skills for Android (I'm a noob at programming) and could use some meaty, and somewhat easy, subject matter to work with. Having a result that is relevant and useful?...bonus.

I could stand to see money and power conversions.

I use www.xe.com to figure monetary conversions and for hp/torque conversions ... http://www.onlineconversion.com/