TABLE OF CONTENTS All length dimensions in the industry and the sciences are expressed in magnitudes based on the standard unit of dimensional measurement, such as the international inch or the meter.
The basic reference unit is the international meter bar. It, along with authoritative duplicates, is available as the primary standard of length to a limited number of national standards laboratories. Today the use of a specific light wavelength as the international basic standard of length has increased the number of sites in possession of an absolute standard. However, the high cost of equipment necessary in making measurements based on light wavelength has made this method prohibitive for most manufacturing settings.
Although theoretically it is conceivable that all gages used in manufacturing and inspection should be checked by using basic measuring standards, considering the millions of gages in continuous use at all levels of industry, such a procedure would obviously be impractical.
Therefore, these primary standards must be used to calibrate high quality secondary standards that are close replicas of the former. These secondary standards form the basis for the creation of a dependable link between the basic standard and the instruments actually used for the measurement of industrial products.
Considering the inherently narrow gaging range of high magnification comparator instruments by means of which precise comparison can be made between the lengths on physical objects and the reference pieces, the latter would have to be available in very small increments, such as 1/10,000...
