On-screen calculators reduce the reliance on pencil and paper for common calculations. They also eliminate the need to memorize complex formulas.
About the examples
Here is an on-screen calculator. This one is designed for photographers. This calculator differs in that all the values are contained in drop-down lists, thus eliminating typing errors.
Here is a mobile version of the Photographer’s calculator. It is designed to display on an iPhone. You can open it using Safari on the PC or Mac (just be sure to make the window thin.).
This example was built using Adobe Dreamweaver and jQuery.