When does a material setup have to be carried out?

In order to be able to achieve optimum guiding results, a material setup must be carried out during / after the following work:

During the initial commissioning of the web guiding system
With optical edge sensor (IR 2011, IR 2012): After changing over to a material with other contrast characteristics (e.g. film with a different material transparency)
With ultrasonic edge sensors (US 2010): After changing over to a material with different sound absorption properties
After cleaning a dirty sensor