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.
A positive z-score means the data value is larger than the mean. If a data value has a z-score of 2, that tells us that this data value is 2 standard deviations larger than the mean. A negative z-score means the data value is smaller than the mean. If a data value has a z-score of â3.1, then this data value is 3.1 standard deviations smaller than the mean. A z-score of zero means that the data value equals the mean. For example, consider a data set with a mean of 50 and a standard deviation of 2. If a data value also is 50, then the z-score is: