I got fed up with the default Windows calculator, and a physical calculator isn't convenient when I'm drawing something in a CAD program, so I cooked up a very basic calculator program. It's got large digits and responds to the numeric kepad keys only. DEL clears the display, INS toggles between +/- and ESC quits. It's capped at 5 d.p. accuracy, which should be enough for most jobs, and can only do +,-,*,/ operations. Basic, but useful.
A ZIP file is available here which contains the executable and VB6 source code. You will need the VB6 runtime installed - see http://support.microsoft.com/kb/290887. The font used is Calibri, so it may display a wee bit funny on older computers.