Malgas

Trusting a recipe to give you the exact timing for something with as many uncontrolled variables as home cooking is not actually any less insane than eyeballing it. The real lesson is: learn how to test for doneness.

One way of doing this for jams and jellies is to stick a plate in the freezer before you start and then drizzle a little on the cold plate when you think it might be done to see if it sets.

Dies the Fire, by S.M. Stirling.

It’s not a measure of efficiency per se, but efficiency is a limiting factor:

In order for a solar panel to put out 1000x more power, the baseline you’re comparing it to must be at most 0.1% efficient, because otherwise the new thing would have greater than 100% efficiency and that isn’t possible.

And that’s a purely thermodynamic argument. The actual limit for solar efficiency is likely less.