Simple Calculator — Copyright © Dec 2007-2018 Mike Cherim. Some rights reserved. Validate: XHTML 1.0 | CSS 2.0 
Something like this would only rarely be needed on a web site, but if you did want to provide a basic four-operation (can be added to) calulator as part of a site or application, this might just might work out well. Copy, paste, and style, and that should be it.
Get the XHTML, CSS, PHP, source. Go to back to the Mike’s Experiments index.