A more capable replacement in the store for free would make up for this. I usually install gimp, but rarely use it for more than quick crops and some brightness adjustments. So, lighter than gimp, more capable than paint...
Use the PowerToy calculator from Windows XP. You can either run it in compatibility mode or patch it so that it doesn't check the Windows version (exercise left for the reader).
Alternatively, use a third-party program like SpeedCrunch.