The PDM system is capable of measuring the Illig wert as invented by Hans Illig from the Daimler works in Mannheim. The Illig wert is an automotive standard for measuring the change in surface cleanliness.
For details on the method as used by Hans Illig please see the article at http://www.sauberkeit-und-reinraum.com. As mentioned by Mr. Illig
- „Partikelzahl gewichtet+normiert auf 1000cm² und 1Stunde“ provides the base to the number.
The direct link is implemented here.
Further information from Mercedes can be found here.
On page 20 of this PDF the whole artice can be downloaded