Engineering Explained lays it out
I find buying motor oil extremely confusing. There are so many numbers and letters involved and I have no idea what any of them mean, much less whether I should buy synthetic or conventional oil.
Fortunately, Engineering Explained is here to lay out exactly what's what - 'SAE' ratings, 'W' ratings, viscosity, and the relative merits of synthetic and conventional oils.
There's a neat viscosity demonstration, too, which has got me thinking that maybe I should check my car's oil more often. I've had my current car since February and checked the oil once. Which is really isn't often enough. But then, I would rather sell a car than service it.