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In a paper presented at the 1993 annual TAGA meeting, Voglesong reported that measured densities of ink-on-paper samples made with 0/45 geometry did not agree with values obtained using 45/0 geometry (1). In a 1985 paper, (2) Clarke & Parry reported that 0/45 and 45/0 geometry reflectance measurements agreed within the 50% confidence level of their measurement system. While Clarke and Parry used a reflectometer configuration similar to that used by Voglesong, they only did measurements of white reflectance standard materials. We are investigating this phenomena using both an apparatus similar to that of Voglesong, Clarke, and Parry, and the fiber optic coupled configuration used in the Byk-Gardner spectrocolorimeter. In both configurations, we are using small integrating spheres in the source and detector channels to insure that effects of polarization, optical element placement, and changes in source-sample-detector geometry are minimized. In this work, the switch from 0/45 to 45/0 geometry is accomplished by physical exchange of the detector and light source at the entrance ports of the spheres - the sample and/or the detector and source optics are not moved as was the case in the previous cited work. We are investigating this phenomena using both an apparatus similar to that of Voglesong, Clarke, and Parry, and the fiber optic coupled configuration used in the Byk-Gardner spectrocolorimeter. In both configurations, we are using small integrating spheres in the source and detector channels to insure that effects of polarization, optical element placement, and changes in source-sample-detector geometry are minimized. In this work, the switch from 0/45 to 45/0 geometry is accomplished by physical exchange of the detector and light source at the entrance ports of the spheres - the sample and/or the detector and source optics are not moved as was the case in the previous cited work. We are doing further investigation using our two apparatus configurations to determine if the previous reported lateral diffusion errors (3) are affected by the use of 0/45 and 45/0 measurement geometries. (1) W.F. Voglesong, Reversibility of 0/45 & 45/0 Reflectance Geometry, 1993 TAGA Proceedings (2) F.J.J. Clarke and D.J. Parry, Helmholtz Reciprocity: Its Validity and Application to Reflectometry, Lighting Res. & Tech., 17, 1 (1985) (3) D.L. Spooner, Lateral Diffusion Errors Caused by Layered Structure of Graphic Arts Products, 1993 TAGA Proceedings.