The distinction between REAL VALUE and NOMINAL VALUE occurs in many fields. From a philosophical viewpoint, nominal value represents an accepted condition, which is a goal or an approximation, as opposed to the real value, which is always present. Often a nominal value is de facto rather than an exact, typical, or average measurement.
* 1 Measurement
See also: Nominal size
In measurement, a nominal value is often a value existing in name only; it is assigned as a convenient designation rather than calculated by data analysis or following usual rounding methods. The use of nominal values can be based on de facto standards or some technical standards .
All real measurements have some variation depending on the accuracy and precision of the test method and the measurement uncertainty . The use of reported values often involves engineering tolerances .
One way to consider this is that the real value often has the characteristics of an irrational number . In real-world measuring situations, improving the measurement technique will eventually begin yielding unpredictable least significant digits. For example, a 1-inch long gauge block will measure to be exactly 1 inch long until the measuring techniques reach a certain degree of precision. As techniques improve beyond this threshold, it will become clear that 1 inch is not the real value of the gauge block length, but some other number approximates it.
In various subfields of engineering , a nominal value is one for which the "name" for the value is close to, but not the same as, the actual value. Some examples:
* For dimensional lumber in North America, a "two by four" is not 2
inches by 4 inches, but rather between 1⅜ and 1⅝ inches thick and
between 3⅜ and 3⅝ inches wide, sized to the equivalent rough hewn
piece of softwood for nominal structural design purposes. The ⅛-inch
tolerances absorb the natural variation.
Other cases involve diameter, speed, and volume.
Sometimes the word "nominal" is misused in engineering contexts as a synonym for "normal" or "expected"; for example, The rotor resistances on all the other operating wheels are nominal.