Let us give a panoramic view of Metrology to begin with and then proceed with detail issues in the next posts.
Lord Kelvin, the renowned scientist, had the following to say about metrology:-
“When you can measure what you are speaking about and express it in numbers, you know something about it, but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind”.
Measurements have been carried out by humans for as long as civilization has existed. From the primitive population who lived in caves to modern man, the need has always been there to measure and know. Of course, all these measurements were approximate. With the development of civilization the need for more acceptable measurement grew. This led to the evolution of the standards of measures. For example, the standard of length evolved from the foot of the “King”, to the Egyptian cubit, to the metallic metre and finally to the monochromatic, highly stabilized light source. Interestingly enough, even though we can now measure with much greater precision, the measurements are still “approximate” and will always have an element of “uncertainty”.
Traditionally, dimensional metrology has been viewed as just another area of measurement science and dimensional inspection has been considered a non-value-added quality control activity in the manufacturing community. The most important change in the way dimensional metrology is applied today is to move advanced geometrical metrology upstream in the product development cycle, where it can support the most significant decisions, i.e. the determination of the specifications used to ensure correct functionality and the design of the processes used to manufacture the parts, rather than downstream where it can only support process control of processes that may or may not be inherently capable and simple pass or fail decisions against a specification that may or may not be functionally relevant.
The dimensional metrology field is made up of three sub-disciplines: Linear metrology, angular metrology and geometrical metrology. Linear and angular meteorology are mature areas with no conceptual developments in several decades, whereas geometrical metrology is rapidly developing areas. We will investigate in detail in the next posts about geometrical metrology.
 http://www.hn-metrology.com/Taking%20Dimensional%20Metrology%20to%20the%20Next%20Level.pdf – Taking Dimensional Metrology to the Next Level Speaker/Author: Dr. Henrik S. Nielsen