The measurements don't even have to be exact. There was a program that taught women in developing countries to make oral rehydration solution for their childre

The measurements don't even have to be exact. There was a program that taught women in developing countries to make oral rehydration solution for their children - the result was decreasing deaths due to cholera by an order of magnitude. Many of these women didn't have tools for measuring the ingredients, and the program didn't distribute them - requiring such tools would restrict the spread of the program. The heuristic is a liter of water, a handful of sugar and a generous pinch of salt. The result may not be exactly the optimal concentration, but it's essentially always close enough to have the desired effect. This heuristic has saved millions (probably tens of millions) of lives.