I am working of the Diesel Emission Project, however i have some problem in evaluating the filtraion power of the Particulate Remover Unit. The following is my question: What is Hartridge Smoke Unit (HSU) ? Could any one can provide some picture of different level of HSU so that I can understand the visual senario of different value (e.g. 25, 50, 100, 150)? Thank you very much for your kind help.