this is kindof gross, but to check your cm for your most fertile days you simply wash your hands, insert two fingers into your vagina and lightly scrape your fingers around to gather some cm. Then you remove your fingers and look to see what your cm looks like and feels like. When you are fertile and ovulating you generally have more cm that is egg white consistency and it will stretch when you pull your fingers apart. When you are not ovulating your cm is scant and a thick, white color. Hope this helps!