oil change issue

I don't proclaim to be an oil expert, but this is what I've learned. According to the Blackstone labs, low temperature ratings are at 100°F and high temperature ratings are at 210°F. The multi-weight oils basically change the shape of the viscosity vs. temperature curve to "flatten" it out. So a 20W-50 oil will be act as a 20W oil at 100°F and a 50W oil at 210°F. The oil still decreases viscosity with rising temperature, just not as fast as a straight weight.