Good or bad roll is very much depending on a product. Often smaller variation is significant for
bulgier grades, like newsprint for example. Densier grades, like coated magazine papers tolerate a
bit bigger variation. If you want to have just one number to follow, the best indicator for a good or
bad roll is COV%. It is coefficient of variation = standard deviation devided by the mean value.
Typically if it is 6% or higher you have bad rolls. If it is smaller than 3, then rolls are very good. But
just a couple of weeks ago one printing house had problems with newsprint rolls even the COV was
just 3,5 about. There was clear softer area in the centre of the roll. So overall profile analysis is
important and ACA offers such services. We can also define tailor-made key values and alarm based
on our analysis about what is good and bad roll in your specific cases.