what is the proper way to measure your horse for a western saddle?

I'm wanting to go to a big saddle shop in Southern Ohio and was wondering if there is a way to get proper measurements for a saddle. I've always had the access to fit my horse with saddle and try out how it fits and sits on her. So buying one for the other horses was easy. But in truth i'm not sure how to just walk into a shop and pick out the right one!

Take your horse with you

http://www.horseforum.com/using-hors...dle-fit-45868/