Lately, it's been hard to escape advertising that tells you to drink your orange juice because orange juice is a good source of folate, which lowers your homocysteine. A plot of homocysteine against folate shows a nonlinear relationship with most of the data bunched in the lower left hand portion of the display. When logarithmic transformations are applied to both variables, the association appears to be linear. If logged homocysteine is 0.88, homocysteine itself is 10 0.88 or 7.58 units. This makes the logs of some numbers easy to calculate.
Every positive number has a logarithm.
You can get the logarithms of numbers that aren't integer powers of 10 from tables or a calculator. The larger the number, the larger its logarithm. Only positive numbers can have logarithms. Give an example of a number whose logarithm is negative. Use a calculator to obtain the common log of some number.