There are dozens of planispheres to choose from but this one is the classic. It has long been our most popular model. That's because this easy-to-use starfinder is a favorable choice for dialing up the night sky for any date and time. The durable plastic 10" wheel won't be affected by moisture and slips into a protective case when not in use. A great travel companion -- keep one handy in your car. Model 40 - 35-45 degrees latitude - most of the continental U.S.