Calibration ratings

[Phrans]

During the calibration process, you get the (technical) message:
"The calibration succeeded with an average delta E of 2.1"
The 2.1, that is my reward for calibrating a transparency.
(I get 1.5 for calibrating a reflective).

Questions:
1. What does the expression mean?
2. Are these numbers ok? In which range should they be?
3. How can one influence the 'average delta E'?

[LSI_Morales]

Hi Phrans,

Delta E is a deviance value. The smaller the number the better.

They should be in ranges between 0 and some positive value. Again the smaller the number (the closer to 0) the better.
If the delta value goes beyond 4, you should get new targets.

You can not directly influence on this values because this is a process taking place internally in the scanner/software.

However indirectly this can be influenced by:

Having a high quality scanner (generally here the rule "you get what you pay for" applies), better components means less and weaker hardware changes.
Warming up the scanner before calibrating and before final scans for any job, meaning, you should perform some pre-scans for 5- 10 minutes before this important tasks.
Changing the calibrating targets every 2 or 3 years.

Cheers