GREG has space reserved into internal buffers for the user's data. Four buffers are available, those with conventional names X Y Z and the Regular Grid array. Buffers X and Y are one dimensional arrays used to store the X and Y data for graphs Y=f(X) (or pairs (X,Y) in some applications). Z is also a one dimensional array and is used for storing additional values such as error bars corresponding to the X (or Y) data. The Regular Grid array is a two dimensional array used to store regularly spaced data (maps) for two-dimensional applications like contouring. Additional buffers are used for specific applications, such as the Polygon buffer.