> If you combine the rule of 72 with the powers of two, then you can quickly find out how long it will take for a quantity to increase by several orders of magn

> If you combine the rule of 72 with the powers of two, then you can quickly find out how long it will take for a quantity to increase by several orders of magnitudes. This seems to me like good but dangerous advice. I'm all for using back-of-the-envelope estimations as "small angle approximations" where they're not far off, but, in general, iterating the lossy approximation to get a large-scale answer is the wrong thing to do. It works well here, but only because we're dealing with logarithms, which genuinely do convert multiplication to addition, and not mentioning this point seems to tempt one to use it in situations where it's not applicable.