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The distinction between real versus nominal value occurs in many fields.
Engineering
In various subfields of engineering, a nominal value is one which where 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 1½ in × 3½ in.
- Mains electricity is nominally 230 V in the European Union, but is allowed to vary ±10%. In North America, the nominal voltage is 120 V, with variance allowed from 114 V to 126 V (±5%).
- NiMH and NiCd rehargable batteries have a nominal voltage of 1.5 V, but actually supply 1.25 V.
- 56 kbit/s modems cannot exceed 53.3 kbits/second.
Other cases involve diameter, speed, and volume.
Sometimes the word "nominal" is also used in engineering contexts as a synonym for "normal".
Economics
In economics, "nominal" values are the "face value" of currency over long periods of time (years), whereas "real" values have been corrected for inflation.