With this easy-to-read monitor, keeping track of the UV index is simple. The dial categorizes the UV index based on a rating of low to extreme and a range of 1 to 11. The higher the index reading, the more precautions are necessary when in the sun. Device works when placed in a sunny, outdoor location using the stand, keyhole hanger, or nylon strap and buckle. Uses 3 AA batteries. 7" diameter.