Calibration, true value and measurement error
When the entire product is produced in a single factory, the main components, gauges and disposable machines work. Modern global supply chains require different systems.
We do not have a physical body part, but a drawing or a digital CAD model. The specified tolerances ensure that the parts are assembled together and executed as expected. Instead of each manufacturer comes to a single main part to set their gauges, their measuring instruments are calibrated. The instrument is then used to set up the production machine and check the parts produced.
All the quality depends on the calibration process.
The most important concept of understanding is that all measurements are uncertain. If I ask you to estimate the height of this text, you might say "about 4 mm". The use of the word "about" means that your estimate has some uncertainty.
In fact, we will never know the true value of anything, all the measurements are actually estimated, and there are some uncertainties. The difference between the measured result and the true value is the measurement error. Since we do not know the real value, we can not know the error: these are unknowable numbers.
All we can quantify the world around us is the result of the measurement, which always has some uncertainty, even if this uncertainty is very small.
If you estimate the height of this text as "about 4 mm, give or take 1 mm", then you have now allocated some restrictions for your uncertainty. But you still can not be 100% sure it is true.
You may have some confidence, such as 95%, which is true. If you want to increase the limit, say or give 2 mm, then your confidence will increase and may increase to 99%. Thus, uncertainty gives some boundaries, and we have one such boundary, the real value.
Well, philosophy is over!
In future posts, I will expand these ideas and how to calculate the uncertainty of a particular set of confidence levels.
