One of the better sites for learning about pull-pull is Alan's hobbies, go to http://homepages.ihug.co.nz/~atong/ and scroll down to pull-pull. Once you understand the term Ackerman (covered in the suggested site) and do a couple installations, you will probably always use pull-pull on the rudder and elevator on your planes. If you always use a little bit of positive Ackerman you can do a lot with pull-pull including routing lines around obstructions, having easily adjustable/variable throws and many other features with very little weight and great reliability. If you can get a copy of an old May 1993 issue of Model Airplane News, there is a good article on how to make your own Giant-Scale Pull-Pull system easily and inexpensively.