Easily proven, the 20/80 rule of PP..
Simply find out from PP materials/call or write to them if you can't find the subject in the materials. Re: "contact" rein diminishing horses' mouths, the proof of the veracity of the statement is given only by the horse itself! The only way one is going to know anything for sure is to listen to & learn from the horse! Tom Dorrance said that everything he learned, he learned from the horse! You might ask why I post, then: I post in the hope that people will check out a subject of horsemanship with their horses, because they care enough about them to want to be 100% sure that they're doing the right thing with them.