Scientific Calculator for UMPC or Tablet PC.

I use my TabletPC on.. oh... an hourly basis. Few things keep me off of it, but one thing is driving me nuts. I can't find touch screen software such as a scientific or finance calculator. I can use the simple calculator, but the buttons are so small that I mash one or another periodically and it makes the reliability of my calculations suspect. There is also the fact that it isn't very powerful.