If you're like me, and hate coding sprite data tooth and nail by hand, or drawing sprites in anything as primitive as MS-paint (that is, you prefer GIMP or some other professional imaging program), then this will make your job ridiculously easy.

It also has lots of cool little tweaks to get the final grayscale image to come out the way you want, you can adjust brightness and contrast so the sprite you created in Photoshop will come out exactly the way you imagined it would in your game on the calculator screen.