CTE for Glass This is a particularly interesting graph. Often we are asked to calibrate master grids or scale for use in precision optical measuring systems. The scales or grid plates are obviously glass, and often that is all of the information the owner has. It is obvious from the graph that the word "glass" conveys almost no information about the CTE of the gage. The best estimate is somewhere between 0 and 10 ppm/°C, with a correction of 5 ppm/°C applied to the data. Even if the artifact is calibrated the a precision environment of a national calibration laboratory, who will measure very near 20 °C to minimize the uncertainty from thermal expansion, the customer will probably not have the temperature control to use the artifact at an uncertainty anywhere near that stated on the calibration report. | 
