When a compressor pumps one CFM (cubic foot per minute), that means the intake port inhales one cubic foot of free air (air at atmospheric pressure, which is 0 psig) per minute. (Note: A CFM does not mean in any sense the compressed volume.) So the unit really measures the mass of air flowing per minute, not volume per minute, since a cubic foot of free air is a unit of mass.
This second scale has a mean and standard deviation that have been arbitrarily set. A z score, for example, is a raw score that has been transformed to a scale with a mean of 0 and a standard deviation of 1.
1. Use the following format to find a z-score: z = X - Î¼ / Ï. This formula allows you to calculate a z-score for any data point in your sample. 1  Remember, a z-score is a measure of how many standard deviations a data point is away from the mean.2  In the formula X represents the figure you want to examine. To find the Z score of a sample, you'll need to find the mean, variance and standard deviation of the sample. To calculate the z-score, you will find the difference between a value in the sample and the mean, and divide it by the standard deviation.