In a spectrographic workpiece metrology system having an optical viewing window, the viewing window is calibrated against a reference sample of a known absolute reflectance spectrum to produce a normalized reflectance spectrum of the reference sample, which is combined with the absolute reflectance spectrum to produce a correction factor. Examples of the selenium compound include a selenium oxide. Instrumentation consists of plate holders, a compression apparatus and a pilot hole forming device that interlocks with the plate. The system comprises electrical control means arranged to receive the electrical signal output by said generator during operation and to apply an AC control signal to said electric motor whereby the compressor is driven at least in part by an output torque of the turbine via the electrical connection therebetween. The position or focal length of the UV light curing head may be varied to maintain focus of the UV light on the ink on a contoured surface of the substrate.