In case anyone was wondering, in my recent discourse with one of my companys' process engineers we were discussing how oil viscosity is rated. It's really a fairly primitive method. Basically a test sample of a controlled size is taken and heated to a specific temperature, then poured through an orifice of a known size. The viscosity rating is how many seconds it takes the sample to flow through the orifice.
For example if one gallon of oil at 150 degrees F is poured through a .250 opening and it take 30 seconds to flow through, then it is rated at 30 weight. Like I said, it's fairly primitive but it's still the method that refineries use.
