Hi Peter. We have a video on our site that explains this pretty thoroughly. This can be explained in text, but it is much easier to show. Take a look at the video and if you still have questions after that let me know.
http://www.flandersscientific.com/index/pg89484
Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com