As I said, the concept of Significant Figures ("sig figs") is associated with rounding, but there is more to it. It also describes the amount of uncertainty there is in a value, and is tied to that value's accuracy and precision. They are the digits in a value that are considered to be important, as a result of the precision in their measurement.

Here are a few basic examples:

- A thermometer reads 26.9 degrees Celsius. This is 3 sig figs.
- A scale displays a weight of 31.22 g. This is 4 sig figs.
- A stopwatch shows 58.778 seconds. This is 5 sig figs.

So far, so good, right? Now, let's throw in a wrinkle. Sometimes, you don't count a zero as a Significant Figure. You ignore them ONLY IF they are at the very start of a number, such as before a decimal place, or at the very end of a number, such as 10.

Here are some more examples:

- The number 0.232 has 3 significant figures.
- The number 0.0076 has 2 significant figures.
- The number 0.000000000000003 has 1 significant figure.
- The number 100 has 1 significant figure.
- The number 82000 has 2 significant figures.
- The number 3,758,200,000,000,000 has 5 significant figures.

So, with those examples, you can hopefully now see how many significant figures a number with just a quick look.

Read on, where I will outline the general rules for determining the number of sig fig's, and also rules on how to do math with them.