There are many methods used in engineering analysis and they are often displayed as histograms to give a visual of the data as opposed to being just numerical.
In 1654, the Slide Rule technique was developed by Robert Bissaker for advanced data calculations.
The integration of computers and calculators into the industry brought about a more efficient means of analyzing data and the beginning of engineering statistics.
Ideally, all products will have the exact same specifications equivalent to what was desired, but countless imperfections of real-world manufacturing makes this impossible.
The goal of Six Sigma is to ensure that the acceptable specification limits are six standard deviations away from the mean of the distribution; in other words, that each step of the manufacturing process has at most a 0.00034% chance of producing a defect.