MiniCalc

iCalc 1.0 is a small, free calculator that allows you to write formulas, which you can leave in its inbox and reopen later with just a click. MiniCalc 1.0 will display results of up to 20 digits, and you can choose to view up to 12 decimal places if you want really precise results. You can have as many MiniCalcs simultaneously opened and/or minimized as you want.