Every scientific calculator has both. Picking the wrong one gives an answer that is off by a factor of 2.303.
If you have ever stared at a number on a form and wondered where it came from, you are not alone. Every scientific calculator has both. Picking the wrong one gives an answer that is off by a factor of 2.303.
log(100) = 2 because 10² = 100. Used in engineering, decibels, pH.
ln(e²) = 2. Used in calculus, compound interest, physics, statistics.
log(x) = ln(x) / ln(10) ≈ ln(x) / 2.303.
Why is ln 'natural'? It's the integral of 1/x dx, falls out of calculus naturally.
Can log be negative? Yes — log(0.1) = −1. log of zero or negative is undefined in real numbers.
Whatever number you land on, sanity-check it against a second method or a quick estimate in your head.