Notations in M letter sizes ranging from 20M to 1.6M for testing at various distances. Each page it’s own contrast level at 100%, 2.5% and 1.25% . This flip book is the smaller version of the Cat. No. 2125. Cat. No. 2180 includes three levels of contrast sensitivity; Acuity, 2.5% and 1.25%. This contrast flip book is great for the use in clinical trials and research studies. It is printed on opaque, high-impact polystyrene and is washable. The test chart is also bound and includes instructions and recording forms. Each level uses traditional Sloan optotypes in an ETDRS format for an equally difficult test from beginning to end. Every level uses a different series of optotypes to help reduce any possibility of memorization. Also, each contrast sensitivity level is highly calibrated and will produce accurate results. This flip book is an excellent choice for research because of its accuracy and reliability.