The values in a Surfer GRD file are recognized as Component 1 (or "C") in Voxler. The “Z” value in a Surfer GRD file can be any variable, (i.e. temperature, the concentration of an ore body, or pollutant), and not necessarily the Z value in XYZ space. To display the Z values at the same scale as other objects, import the grid using the curvilinear lattice options.