Try a USB numeric keypad. I got one at Staples. It has a built in calculator
with the ability to send numbers directly to the computer, where your cursor is.
Very handy at tax time. ;)

Could use the calculator app and copy and paste, but the keypad doesn't get in
the way of other apps, nor get hidden behind them, and it has a single button to
send whatever's on its calculator display to where your typing cursor is.

It also works as a calculator when not plugged into a USB port, automatically
switches to keypad mode when plugged in, use the Mode button to switch to
calculator.

Model # 14573