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## Accuracy and Precision | Accuracy Vs Precision

In this article “Accuracy vs Precision” we will try to learn about accuracy and precision. It is difficult to explain the difference between Accuracy and Precision in general terms, because as far as the meaning of the words is concerned, the meaning of these two is almost the same. But in the measurement process, Accuracy and Precision are completely different words and they have different definitions. **Click here** **to read this article in Hindi**

## Accuracy | What is Accuracy ?

Accuracy is that quality of a measuring instrument, which shows the closeness between the measured value of a quantity and the true value of the quantity, that is, the closer the value measured by the instrument is to the true value, the more accurate the instrument and its The accuracy will be higher as well. Thus, accuracy refers to closeness to true value.

Accuracy can be demonstrated by a variety of methods. For example, we can show this by limits of error in measurement or inaccuracy. Also Accuracy can be expressed in point accuracy, as a percentage of the scale range of the instrument, or as a percentage of the true value of the quantity measured.

### 1.Point Accuracy

It is the accuracy of the instrument at any one point of the scale. This accuracy does not give information about the accuracy of measurement at any other point on the scale. Point accuracy also does not give any information about the general accuracy of the instrument. To find out the general accuracy of the instrument, a table of accuracy can be made at different points of the entire scale.

### 2.Accuracy in terms of percentage of scale range

If the scale of the measuring instrument is uniform, then its accuracy can be expressed in terms of the range of the scale. For example, the accuracy of an Ohm meter whose scale range is 1 Kilo ohm can be represented by ± 0.01 percent of the scale range. It means when the reading of ohm meter is 1000 ohm then its accuracy is ±0.1% which is negligible. But when the meter reading is 100 ohm then the error is (1000/100) x (0.01) = 1% which is quite large. Thus, accuracy as a percentage of the instrument’s scale range can be misleading.

### 3. Accuracy in terms of percentage of True Value

The most appropriate description of accuracy is given as a percentage of the true value of the quantity being measured. For example, within ±0.01%, ±0.02%, or ±0.05%, etc., of the true value of the quantity being measured. It means that the smaller the reading, the smaller the error.

## Precision | What is Precision?

Precision is that property of measuring instruments, due to which, the instrument reproduces the same measurement on repeated measurements. Precise means clear or ‘sharply defined’. Consider an example to clarify the difference between accuracy and precision. Suppose a voltmeter is very accurate because of its construction because its scale is finely divided to show minute readings, its scale is very distinct and it has a knife to remove parallax. A mirror is fitted with the knife-edge pointer. Let the reading be taken from this voltmeter up to 1/100 volt. With all these properties, it is assumed that its zero-adjustment is wrong. Whenever we take a reading from this voltmeter, it will always be equally accurate. Readings can be taken from this voltmeter up to a minimum of 1/100 volt and each reading will be clearly defined. However, the readings taken from this voltmeter will not be accurate as the zero-adjustment in it will not be true.

Consider another example. Suppose a known voltage of 100V is measured with a voltmeter and the voltmeter shows 104, 103, 105, 103 and 105V readings. It is clear from these readings that the voltmeter is not reliable for more than 5% accuracy whereas it is ± 1% accurate in terms of precision because the different values displayed by it and their average are 104 The voltage difference is only 1 volt (105 – 104 = 1V and 104 – 103 = 1V). Thus this voltmeter can be calibrated for accurate measurement up to ±1V. It is clear from this example that the accuracy of the instrument can be improved by calibration but not the precision. It is also clear from these readings that if all the readings are close but there is some scattering (from 103 V to 105 V), then this voltmeter is good in terms of precision but not accurate.

Thus, when we say that the readings taken by an instrument are precise, it means that the results displayed by the instrument are in agreement with each other. Although there is no guarantee of accuracy just because there is consistency.

### Precision characteristics

The two main characteristics of the accuracy of measurement are-

1. Conformity of results

2. Significant figures

### 1. Conformity of the result

Conformity means getting the same value on repeated measurements of a quantity. It is also called ‘consistency’ of measurement. If the results obtained by the instrument are confined to a tight cluster on the scale, then the precision of the instrument is high. On the other hand, repeated measurement of the same quantity in a low-precision instrument would be limited to a relatively large portion (broad scattered) on the measurement scale. Are. But high precision does not mean that the accuracy of the instrument will also be high. Because each measurement is equally affected by any defect in the instrument, the readings deviate equally from the true value.

Precision can also be explained by another example. Let a resistance whose true value is 1,485,6925 ohm be measured by an ohm meter. Ohmmeter shows its correct value (1,485,6925ohm) on measuring the resistance but we are unable to read its correct value in the meter. In meter we read its value as 1.5 mega ohm. It is as close to the true value as we can get to read the scale as accurately as possible. Although we get the same value on repeated readings of the scale, it is not true. The error in this observation is limited by the scale. This error is due to lack of precision.

### 2. Number of Significant Figures

The precision of the instruments also depends on the number of significant figures in the value shown by it because the significant figures show the dimensions of the measurement and the precision of the measurement. The greater the number of significant figures, the higher the precision of the measurement. For example, if a voltage is set at 12V, then its value should be taken as close as possible to 12V, not 11V or 13V. If the voltage is 12.0V, it means that it is closer to 12V than 12.1V or 11.9V. The number of significant figures in 12V is 2 while the number of significant figures in 12.0V is 3. Hence the number with more significant digits (12.0) exhibits more precision than the first number with less significant digits (12V).

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Accuracy vs Precision-Author(Theinstrument Guru)

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