Select a group of numbers that include negative and positive numbers. Use --5, -2, 0, 3, 10 for your first RMS calculation.
Square each number to be averaged; multiply each number used by itself. For this example, the results are 25, 4, 0, 9 and 100, since--5 times --5 is 25, -2 times --2 is 4, 0 times 0 is 0, 3 times 3 is 9 and 10 times 10 is 100.
Total the squares. Conclude that the total of the squares is 138, since 25 plus 4 plus 0 plus 9 plus 100 is 138.
Calculate the average of the squares. First, count how many number values are used to calculate the average. Conclude for this example that the number of values used is 5.
Divide the total obtained in step 3, 138, by the number of values used, in this case 5. Conclude that the average of the squares is 27.6, since 138 divided by 4 is 27.6.
Take the square root of the average of the squares; use the square root key on your calculator. Conclude that the RMS value for your first calculation is 5.26.