This Glass-Chek Test Instrument measures the thickness of both lites of glass, as well as the air space of an insulating glass window assembly. Simply press the GC1000 Glass-Chek Meter against a single lite of glass, or a dual lite window assembly, push the button and hold it until the measurements are digitally displayed. The thickness of each lite of glass, the air space, and the overall thickness of the I.G. unit will simultaneously appear on the 2-line liquid crystal display. Unit can be read in decimal, fractional and metric. For best results clean the window prior to testing. Uses one 9 VDC battery (included). Digital Readout Laser Accuracy Factory Calibrated, Needs No Field Adjustments.