it's a good idea and worked for us, but as others noted it's a very manual, and thus error prone, way to track this. my wife now uses an iphone app which is much easier to use and is also far less expensive.
i recommend skipping this product and getting something digital to do this for you which will automatically track your fertility, estimate your next fertility, etc. if you have an iphone i recommend "ova" which is the app my wife uses. It is easy to use and has great fertility tracking and extra features.Get more detail about Cycle Beads for Ovulation Prediction.
