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.
Here is a typical portion of such a table. (Note that the z-score we are to look up in the table changes every time this page is loaded.). An alternative arrangement, the list arrangement, gives the possible z-scores along with the table associated value.eading Normal Distribution Tables. A common approach to this is the  cross-table  arrangement. Here we break the z-score into two parts, the left part is usually the units and tenths digits and the right part is the hundredths digit. Thus, a z-score of 2.41 becomes 2.4 and 0.01.