The CRL Glass Gauge Pro measures single and double glazed units, and it also measures individual glass thickness. It will help in the identification of laminated glass, and is a must for determining the thickness of shop front glass. It has ball tips on the ruler and gauge body so doesn't have to be square on to the glass, very useful when hanging out of a first floor or higher window to guarantee maximum accuracy. The ruler is printed on both sides which is ideal for left, right and top hung windows, and cannot fall out. When not in use there are no parts protruding. It is made from glass filled polymer, cannot scratch the glass, and is virtually indestructible.