From the Latin, consistent means “standing firm.” Today, the word is synonymous with stable, constant, regular, or lacking in deviation.
What is of interest to the quality engineer about consistency is that it allows things to be measured and even predicted. There are things about the natural world that are consistent and, therefore, can be measured and predicted. The movement of the earth is so consistent that we have been able to measure its movements to define the date and time. We have even reached a point where an app on our phone can tell us the precise time the sun will rise in the morning. Knowledge, observation, and technology allow us to measure the natural cycle, more commonly known as “the weather.” Doppler radar and weather stations have given us a leg up on detecting impending weather events, ones that can wreak true havoc such as hurricanes and tornados, and give us a fighting chance to warn those in the path of the destruction.