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.
If a z-score is equal to 0, it is on the mean. If a Z-Score is equal to +1, it is 1 Standard Deviation above the mean. If a z-score is equal to +2, it is 2 Standard Deviations above the mean. If a z-score is equal to -1, it is 1 Standard Deviation below the mean. If a z-score is equal to -2, it is 2 Standard Deviations below the mean. In our example, your score was 98%. This raw score had a corresponding z-score of +1.24. The value of this z-score tells us that your raw score of 98% was 1.24 standard deviations away from the mean.