For color measurements, the visual difference percentage is a convenient way to evaluate the calibration accuracy.

Measurement data is displayed in paper relative density units (Status T). The Fiery Server calculates the visual difference percentage using the Murray-Davies formula, which takes into account the exponential nature of density measurements.

If the measured maximum density is less than the target maximum density, it means that the printer is currently performing lower than expected using this calibration setting. A printed output at 100% of this colorant does not result in the maximum density that this type of printer is expected to print. This situation is acceptable in many proofing situations, because simulated CMYK color spaces typically do not require the maximum density that the printer is capable of.

If the measured maximum density is more than the target maximum density, it means that the printer is currently performing higher than expected using this calibration setting. To meet the calibration target, the Fiery Server does not need to specify 100% of the colorant. However, the full gamut of the printer is not being used.

An application such as Adobe Photoshop uses units of percentage from 0% (paper white) to 100% (maximum density). Assuming the output profile used in Adobe Photoshop matches the calibrated state of the Fiery Server, a visual difference of -5% for cyan means that the printer cannot produce the cyan color values specified in Adobe Photoshop between 95% and 100%. A visual difference of +5% for cyan means that the printer can produce all the cyan color values specified in Adobe Photoshop, and could produce up to 5% denser cyan values as well.