For offline use, save the unit conversion programme to your harddisk by clicking on the screenshot below. Select "Open" rather than "Save", if you are asked. You will see the "Java™ Web Start" symbol for a few seconds. The unit conversion programme starts automatically. If not, it might be necessary to update your Java™ installation.
You will find a link to your local copy of the unit conversion programme by opening a Java™ Web Start window. Select "View Downloaded Applications".