**Standard deviation** measures how close our numerical data points are to one another and to the “true” value.

**Concept:** Understanding Standard Deviation

We're going to say that the standard deviation, so standard deviation, measures how close data results are to the mean or average value. We're going to say sometimes it's easy for us to look when we have a few numbers. We just simply look to see how close they are to one another, how close they are to the true value. But sometimes, we may require some help. That's the whole basis for standard deviation.

This is going to become an important idea when it comes to accuracy and precision in this chapter and also when you take your lab. Because when you're doing labs, labs are all based on how accurate and how precise can your measurements be when doing any of the experiments that you have to do.

We're going to say here, the equation for standard deviation is the square root, where we have the summation. This is sigma, the summation of x1 minus x squared divided by n minus one. We're going to say that x or x1 is simply a measurement. We're going to say that x with a bar on top of it is our mean or average of all the measurements added up and divided by the total number of measurements. This is our mean or average. Then we're going to say n, n represents the number of measurements that we have.

The equation might seem a little bit intimidating, but it's really easy as long as you can remember what it is and how do we plug in the numerical values that were given.

**Example:** Calculate the standard deviation for the following results: 5.29, 5.35 and 5.31.

**Example:** Calculate the standard deviation for the following results: 0.039, 0.061 and 5.3 x 10** ^{-2}**.