Originally Posted by Helen B
However, the relative log values of the step tablet densities, which are plotted on the X-axis, are being used to determine the the configuration, or slope, of the curve on the y-axis. If the two units are not calibrated by measurment with the same mode, or color of light, it would appear to me that the CI of the curve would be either artificially expanded or contracted (slope increased or decreased), assuming of course a difference in measurement with different modes.
This situation does not exist when we work with traditional developers that yield neutral tones because the measurment system for both the original step tablet and the test strips is the same.
And just for the record, there is often a difference between UV and Visual channel measurements of reference step tablets. For example, one of my Stouffer TP 45 step tablets measures as follows. In Visual mode, Step 1 = 0.05, Step 11 = 1.50, and Step 21 = 3.05. In UV mode the measument is, Step 1 = 0.10, Step 11 = 1.45, and Step 21 = 2.87.