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.
z-scores, returned as a vector, matrix, or multidimensional array. A vector of z-scores has mean 0 and variance 1. If X is a vector, then Z is a vector of z-scores. If X is an array, then zscore is an array, with each column or row standardized to have mean 0 and variance 1 (depending on dim).