ken you can buy little diagnostic gadgets that connect to the OBD port. some of them have DPF information that will tell you the live soot level that's in the filter but you havta make sure your car is compatible with the gadget. they're brilliant so you can stay on top of the situation. Bring it on the motorway and you'll see the soot level in the filter dropping on the screen 13.8 grams, 13.5 grams, 12.8 grams etc. using dipetane at every fill up really helps the combustion process. i use it religiously but they've been out of it at Halfords the past two weeks. filling the tank up with just petrol you really notice the lack of oompf my car has.