Not sure, I thought it was measured somehow but ??
Looks like I might have remembered correctly. Did a quick search and found this.
"I sent Blackstone a virgin sample of Audi 0W-30 fully synthetic oil. It was clearly labeled as Virgin 0W-30 oil. As you can see from the report below, they thought it was a 10W-30, but also stated it could be a thick 5W-30 or a thin 0W-40. I wonder what that tech had been smoking.
I have no problem with the cSt 100C being 10.67 (if that's what it really was). But I don't like the fact that they have decided to come up with their own standard for a 30 viscosity oil in the cSt 100C test. They say it should be 9.9-11.9. This is NOT THE SAE STANDARD. According to every source I have consulted, the SAE standard for 30 viscosity oil is 9.3-12.49. According to Blackstone's "30 grade standard", Mobil 1 ESP 0W-30, with a cSt 100C of 12, would be a 40 weight oil.
It should also be noted that the SAE standard cSt 100C for a 40 weight oil is 12.5 to 16.29. So there is absolutely no way this could have been a "thin 0W-40".
In the future, I'm using either Oil Analyzers or Polaris Labs for my oil analysis."