I meant 400 micron rated pump or better. On a vehicle you'd be happy with anything under 1000 microns for the system. How many microns are vacuum pumps rated? Oh wait they dont rate them in microns I wonder why? It can be done with the air operated unit if one wishes. A micron guage is nice to have but for those of us who are licensed it makes sense. For the every day joes I guess venturi looks attractive.