Clings to window electrostatically. Simply lift off to reposition or wash window. 7-1/4'' diameter fits all standard windows. Big, readable numbers are in full view. Needs no screws, or tools, to install. Not recommended for windows with plastic film overlay. Never leave mounted on object, such as motorhome or boat, while moving. Remove before getting underway. Full 1 year warranty. Made in U.S.A.