Abstract: A modified infra-red scanning gauge used in measuring the moisture content of a paper-web during manufacture or when subject to a coating practice, has a measurement channel and a reference channel. The measurement channel is based on the infra-red absorption spectrum of water which has an absorption band centered on 1.94 microns. The reference channel is conventionally at a wavelength of 1.83 microns where water has previously been considered to be transparent to infra-red or at a wavelength of 1.68 microns. The gauge is intended for measurement of high water content, where at 1.94 microns absorption effectively becomes total thereby preventing measurement being made, and uses a narrow-band filter of 0.03 micron wavelength offset from the peak of the 1.94 micron absorption band in the range 1.76 to 1.87 microns, previously considered stable as regards water content but now disclosed as showing a water-dependent variation at high water contents. In a specific example a 1.