# Right value

The term correct value is a term from measurement technology and quality assurance , it is closely related to the term true value . The correct value takes the place of the true value when it comes to quantitative information on a measurement result or characteristic value .

## Definitions

The true value (of a measured quantity ) is defined as

"Size value that matches the definition of a size."

- International Dictionary of Metrology (VIM), 2012, No. 2.11

This is clear in terms of its size, but cannot be determined. Therefore there is a further term, the correct value (DIN) or agreed value (VIM), which is defined as

"Size value assigned by agreement of a size for a given purpose."

- International Dictionary of Metrology, No. 2.12

The basic standardization for measurement technology describes accordingly

• the true value of the measurand as the target of the evaluations of measurements of the measurand; it is an "ideal value",
• the correct value of the measured variable as a “known value” for comparison purposes, the deviation of which from the true value is considered to be negligible for the purpose of comparison.

The correct value is also referred to as the conventionally correct value.

This is in accordance with the standards for quality assurance and statistics.

## Applications

### Examples of true values

One of the few true values ​​that are known in physics is the speed of light in a vacuum , which is precisely determined by definition . As an exactly known quantity, however, it is no longer the target of a measurement. When evaluating measurements, no true value of the measured variable is known and a numerical calculation with the value of the measured variable is only possible with a correct approximate value whose deviation from the true value is considered to be negligible for the purpose of comparison. ${\ displaystyle c_ {0} = 299 \, 792 \, 458 \; \ mathrm {m / s}}$

Other well-known true values ​​are for example

• the angle of the full circle,
• a finite number of elements.

### Examples of correct values

In practice, e.g. B. in legal metrology, a measuring device is considered correct if its systematic measurement deviations are within specified error limits .

In the case of a piece of weight, a value of its mass determined for the purpose of calibration is determined by agreement as the correct value - replacing the true value. For this purpose, the correct value is with measuring devices or normal determined whose measurement deviations should be smaller in absolute value by at least an order of magnitude, which is approved for the intended purpose than the amount of measurement error. The value obtained in this way can differ from the nominal value.

The best known value for the electric field constant is given with the uncertainty . If someone wants to calculate the capacitance of a flat plate capacitor , with relative uncertainties of 1% being known, this can also be recognized as the correct value for this purpose . The same applies to all physical constants . ${\ displaystyle \ varepsilon _ {0} = 8 {,} 854 \, 187 \, 8128 \ cdot 10 ^ {- 12} \ \ mathrm {F / m}}$${\ displaystyle 0 {,} 000 \, 000 \, 0013 \ cdot 10 ^ {- 12} \ \ mathrm {F / m}}$${\ displaystyle C}$${\ displaystyle C = \ varepsilon _ {0} \ varepsilon _ {r} {\ frac {A} {d}}}$${\ displaystyle A, \, d, \, \ varepsilon _ {r}}$${\ displaystyle \ varepsilon _ {0} = 8 {,} 854 \ cdot 10 ^ {- 12} \ \ mathrm {F / m}}$

## literature

• Franz Adunka, Measurement Uncertainties: Theory and Practice , Vulkan, 2007
• Bernd Pesch, Measuring, Calibrating, Testing , Books on Demand, 2009

## Individual evidence

1. JCGM 200: 2012 International vocabulary of metrology - Basic and general concepts and associated terms (VIM) . (PDF; 3.8 MB; accessed January 25, 2015)
2. a b c DIN 1319-1, Fundamentals of measurement technology - Part 1: Basic concepts , 1995, No. 1.3 and 1.4
3. DIN 55350-13, Terms of Quality Assurance and Statistics - Part 13: Terms for the Accuracy of Determination Procedures and Determination Results , 1987, No. 1.3 and 1.4
4. CODATA Recommended Values. National Institute of Standards and Technology, accessed July 30, 2019 . Value of the speed of light, CODATA 2018
5. DIN 1319-2 Fundamentals of measuring technology - Part 2: Terms for measuring equipment , 2005, No. 3.7.3
6. Wolfgang Dutschke: Production measurement technology . 4th edition. Teubner, Stuttgart 2002, ISBN 978-3-519-36322-4 , p. 9 ( limited preview in Google Book search).
7. CODATA Recommended Values. National Institute of Standards and Technology, accessed July 30, 2019 . Value of the electric field constant.