276 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Y and Z. It employs the flicker photometer measurement principle, which involves a rapid continuous comparison between sample and standard, giving a direct measurement of the percentage difference in reflected energy. The optical head is linked electrically to the physically separate control console to provide remote control and display. The Colorede has been used on-line in a paper machine (8) and the arrangement of the instrument is shown in Fig. 3. Use of the Colorede measuring system The reflectance values of the standard pattern are obtained by direct reading relative to a white tile these readings are held electronically on the control console and serve as the future standard. The colour difference, •X 1, bY 1 ZkZ 1 • ' ' between the standard values X1 y1 Z1 and the moving substrate, at the end of the production line, is regarded as three simultaneous continuous signals for display on (i) three colour difference meters, (ii) a three pen chart recorder, (iii) the IDL colour analysis display computer. Accuracy of the Colorede measuring system The accuracy of the Colorede as a colour measuring instrument for X, Y, Z values of the ( .I.E. system has been obtained by comparison with an instrument widely used for colour measurement, the Coloreye Signature Large Sphere Model Colorimeter, on a range of shades with reflectance readings from 10-90%. (Table V). Value X Y Z Table V Average difference between Coloreye- Colored e --0.222 0.535 --1.237 95 % Confidence interval --0.682 to 0.238 0.162 to 0.908 --1.530 to 0.944 There is a small, but statistically significant difference between the Cotorede and the standard instrument, but the Colorede can be described as

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