Root mean squared error

Root mean squared error is a way of measuring how well something is doing compared to other things. It's like getting a score for how good something is. To calculate it, you start by subtracting the expected result from the actual result. That number is called the error. Then, you square this error so it's always positive and add up all the errors (you can think of this like adding up a lot of numbers with a plus sign). Finally, you divide this number by the total number of errors, then take the square root of the answer. This gives you the root mean squared error - if the number is low, it means the thing is doing a good job.