This is a pattern which repeats itself endlessly not only with pieces of pie but in manufactured products and in nature. There is always an inherent Variability. Sometimes it�s a matter of finding a measurement device sensitive enough to measure it.
Measurements may be in volts, millimeters, amperes, hours, minutes, inches or one of many other units of measure.
It you take a sample of a population (such as height) and you chart their distribution, you will end up with a curve that looks like a bell.
A Distribution which looks like a bell is a Normal Distribution. Normal Distributions are the most common type of distribution found in nature - but they are not the ONLY type of distribution.
Heights of men in the military:
Average height: 1.80 meters
Shortest: 1.59 meters
Tallest 2.01 meters
Sixty-eight percent are between 1.73 and 1.87 meters.
Ninety-five per cent are between 1.66 and 1.94 meters.