1. 35spf sunblock is practically identical to 70spf sunblock.
2. Going from 10mpg to 20mpg is a better fuel savings than going from 20mpg to 100mpg.
35spf blocks 97.1% and 70spf blocks 98.5% of UV. (1-(1/Spf)). How you apply and how often is going to be greater than 1.4%.
Seems that SPF is a marketing hoax. Same with mpg.
How many gallons will it take to cover 1000 miles with those three mpg ratings?
10 mpg = 100 gallons
20 mpg = 50 gallons
100mpg = 10 gallons
So the first jump saved 50 gallons. The second was only 40. All this despite the apparent 5X advantage. So the MPG isn't that useful when comparing cars. In the rest of the world they flip the ratio over and use the metric equivalent of gallons per mile. Actually they use L/100kilometers. A number useful for comparison purposes.
https://www.youtube.com/watch?v=kMgP0lFyVXA#t=150
