Thickness measurement of transparent substrate

The invention provides a method for determining the thickness of a transparent substrate at a point on the transparent substrate, wherein the transparent substrate is not parallel to an opposite major surface at that point. The method includes comparing an image of a target having at least a characteristic which varies along a dimension of the target. A plurality of thickness calculations can be made to obtain thickness distribution of the transparent substrate on the desired dimension of the transparent substrate. The method can be used, for example, to obtain the thickness of a thick side portion of a glass tape. The thickness distribution can be used to calculate the thickness of the thick side portion, and then calculate the weight of the thick side portion. The flow rate of molten glass can be determined by using the weight. When an actual flow rate is compared with the desired flow rate, the flow rate of the molten glass can be used to control the flow rate. 种在透明基板上的点处确定该透明基板厚度的方法，其中透明基板在该点处的相对主表面不平行。所述