Don Gilham
Model railways, Photography, anything lazy
Now, first off if this is old hat to some people my apologies, but it's the first I knew of it. Please click on the link to save my trying to explain (should be self-explanatory).
http://cs.trains.com/TRCCS/forums/p/203636/2226229#2226229
http://cs.trains.com/TRCCS/forums/p/203636/2226229#2226229