NOTE: If you found this site to be working in the past and it no longer does, it could be because Chrome has now disabled Java applets (plugin) read about it here.
However "Firefox" does support it, and there is no need to download the updates, just jump through all the hoops that firefox throws up.
The calculator on this site is a Java Applet. The developers of Java have changed the security settings, and what used to work no longer does. So in the meantime if the applet fails to load, (Try it first before updating to the latest Java), open 'config Java' from the run or start menu, (or java) from the control panel, on a mac open system preferences. Look for the jave coffee cup symble and change security settings to medium.
This should be all that you have to do. If that doesn't work, add the site to the trusted sites list. (again in the Java Control Panel) The site only does math calculations within itself, so there are no security issues.
Also for Internet Explorer you may have to add the site to "compatibility view".
Else check this out Work around for Blocked Site
or Here (just cancel the applet that comes up.):- another explanation
In the meantime, I'm updating all the programs on this site to another language, and one day I will get around to updating this one.