Delta-E (dE) is the degree of error allowed in colour reproduction. Most companies work to specific delta-E tolerances, and these often differ between companies.

There are many different formulas which can be used to calculate colour difference and you can read more about them here.

Generally the AVA software uses ∆E*ab CIE76 for its calculations for performance reasons, however in ColourSys you can choose from the methods listed by going to the Window Menu and selecting Colour Difference.

This method takes the colour data from each chip within each file and produces the mean and median differences and the difference between them.

It is particularly useful for measuring the difference between two calibration colour books, printed on the same printer, at different times (with a week between them, for example). From the results, you can work out how much the printers colour reproduction drifts in a week. 

Delta-E Lab, CIE dE 94, CMC 1:1, CMC 2:1 and CIE deltaE 2000 are all supported on colour difference calculations. 

Follow the steps below to obtain the difference between your colour files.

1. Open the colour files you wish to compare.
2. From the Colour Menu, select Colour Difference… A sheet will open with the name of the active colour file at the top, and a drop down menu containing the name of all open colour files.
   
3. From the drop down menu, select the colour file you wish to compare to the active one, and click OK. You will be guided through saving a text document, which you can name and save anywhere on your hard drive. 
4. Once saved, navigate to the file in the Finder, and double click on it to open it into TextEdit. Make the TextEdit window larger so you can see all the appropriate data. The chip names, Lab values and delta-E differences for each chip will be displayed. The Mean and Max delta-E differences will be given at the bottom of the document.