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.
We'll begin with z scores. z scores can be computed by equating the mean of the raw score distribution to 0.00 and the standard deviation to 1.00. T-scores are directly related to z scores. With T-scores, the mean of the raw score distribution is equated to 50, and the standard deviation is equated to 10. Therefore, a z score of +1.00 would be equal to a T-score of 60. In general z scores are expressed as decimals carried out to the hundredths place and T-scores are expressed as whole numbers. Thus, a z score of -3.00 is equal to a T-score of 20.