Accuracy definition: It is defined as how close the measured value to the target/true/reference value.
Decisions can be made highly effective if the measurement data have high accuracy and precision. High accuracy and precision in the measurement data can be achieved only if there will be small variations in the measurement system.
Instrument/gage with high accuracy and precision will always lead to better decisions, improve quality of observed/measurement data, and reduce chances of errors.
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Accuracy definition | Accuracy Meaning
Accuracy is the degree of closeness of the measurements to the target or reference value. Precision on the other hand is the degree of closeness of measurements with each other.
The above figure shows that the measurement system/data is accurate as the average of measured values is very close to the target value, but not precise because the spread of measurements is large i.e. measurement values are away from each other.
The measuring equipment must have adequate precision and accuracy. If these two conditions are not met, then the quality of measurement data obtained by the instrument/gage will be poor or low which may lead to wrong decisions and increase the cost of the product due to poor quality.
In MSA and calibration process, the following measurement system variations or errors are measured and controlled to improve the quality of the product and process.
- Repeatability
- Reproducibility
- Bias
- Stability or Drift
- Linearity
Bias often referred as “Accuracy” error whereas Repeatability and Reproducibility often referred as “Precision” error.
Accuracy Vs Precision | Difference
Explore the below link to understand the difference between accuracy and precision with pictorial examples.
Examples of Accuracy
Example-1: Let’s measure the standard weight of 10Kg on weighing scale-1. And the values of the measurement obtained are 10.15kg, 10.20kg, 10.50kg, 11.4kg, and 12.10kg respectively. The result indicates that our weighing scale is Accurate i.e. average of measurements is near to the specified/target value, but not precise i.e. measurements are not a consistent or large variation in measurements.
Suppose if we measuring the same standard weight on weighing scale-2, then we obtained the values of 12.15, 12.18, 12.35, 12.20, and 12.41kg respectively. That means weighing scale-2 is more precise than weighing scale -1 as all values are very consistent/close to each other. But weighing scale-2 is not accurate because the average of measurements is away from the target/reference point.
Example-2: Let’s measure the diameter of the pipe 25mm with a micrometer. The measurement values obtained are 25.21, 25.10, 25.15, 24.10, and 26.15mm respectively. The result indicates that our instrument is accurate i.e. average of measurements is very near to the target/specified value, but not precise i.e. large variation in measurements.
Example-3: Suppose we have an object and let’s say the temperature of the same is 30 deg. celsius. But the thermometer is showing readings 30.5, 30.3, and 30.10 degrees respectively. The result indicates that the thermometer is accurate and precise i.e. degree of closeness of measurements to specified/target value is very high and measurements are consistent in nature.
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