This paper explores some influences on measurement results and means to tighten achievable tolerances. A set of unprinted paper samples including IR3 reference calibration standards was prepared and measured with 5 benchtop instruments (Elrepholike) and 7 hand-held instruments (X-Rite Spectrolino). The samples were selected by surface (uncoated, matte, semimatte, glossy, high glossy) and effect of optical brighteners (OBA, from very low to high fluorescence). The instruments were tested first for their short-term repeatability, then for inter-instrument agreement, which was better for the Elrephos, but could be matched for the Spectrolinos by adjusting for gloss and OBA response. Sample inhomogeneity required multiple Spectrolino measurements to match the Elrepho's XLAV aperture. With these methods and some precautions in calibration, measurements can be translated from one type of instrument to another with tolerances well below 1 ΔE.