The calibration of the spectroradiometer's wavelength scale is often over looked by the users. However it is relatively easy to verify and does not always require expensive equipment. The Field Spectroscopy Facility uses a mercury argon spectral line source with emission lines in the ultra-violet, visible and near infrared spectral regions. They also use a calibrated Mylar sheet with absorption lines between 1.1 and 2.5��m, an erbium doped Spectralon panel with absorption features between 350 and 1500nm and a McCrone glass filter with absorption lines across the visible, near infrared and shortwave infrared spectrum.