arkeros's comments

On: Estimating Logarithms

[arkeros]

You also don't need to remember 7, as 2*7^2 =~ 100 => log 7 =~ (2 - 0.3) / 2 = 0.85

[brucehoult → arkeros]

Yes, as I mentioned in one of my other replies. Or 2400^0.25.

Same for 9: sqrt(81) = sqrt(8 * 10) -> (0.3*3 + 1) / 2 = 0.95

At some point it's easier to remember a few numbers than calculate a lot of formulas.