This is a set of a large triangle and compass used for the Class 1 marine license exam. It includes guide lines helpful for drawing! This is an authentic product purchased at the training center. I bought this about two years ago when I obtained my Class 1 marine license. I only used it for studying and the exam. I disinfected and removed as much dirt as possible, but some dirt remains on the corners of the case. I don't think it will affect your use. If you are trying to get a Class 1 marine license, please consider this!