I frequently found myself doing relative simple calculations over and over again, such as the future value of an investment. A spreadsheet works fine if you always calculate in the same direction (i.e. calculate the future value based on present value, interest and duration), but I usually want to jump around a bit, calculating back and forth between parameters (e.g. what interest rate would be needed to get this future value).

So I wrote a “generic” calculator in JavaScript, that can be configured via query strings in the URL. It’s currently highly beta, so don’t do anything important with it yet. Some examples of what you can do:

If you want to turn these iframes into a widget for use on OS X’s dashboard:

  1. make a directory with a temporary name
  2. save the iframe as calculator.html
  3. add this plist-file
  4. add these two images
  5. rename the directory to end in .wdgt, which will convert the directory to a package.