Real versus nominal value

For the distinction between real purchasing power and nominal value, see Real versus nominal value (economics).

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.


See also: Nominal size

In measurement, a nominal value is often a value existing in name only;[1] 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:

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.[3]

See also


  1. ASTM D3039, D4139, and others
  2. "Basic Tutorials: Solar Panels". Retrieved 2014-06-25.
  3. "Rear Wheel Trouble Continues". JPL. 2009-12-10. Retrieved 2009-12-10.
This article is issued from Wikipedia - version of the 6/18/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.