In the realm of scientific research, engineering, and even everyday life, precise and accurate measurements are crucial for obtaining reliable results. What characteristics make a scale highly precise? What is a measurement that is accurate? Is trueness the same as accuracy? In this article, we explore the concepts of measurement trueness, accuracy, and precision and understand their significance in 3D laser scanning.

Measurement trueness

Measurement trueness is the closeness of the mean value of a large number of repeated measurements to a known value.

Assuming that we have conducted multiple measurements and calculated the mean value of these measurements, if this mean value is close to the reference value, we can say that the measurement trueness is high. Conversely, if the mean value of the measurements deviates from the reference value, then the measurement trueness is low.

Measurement precision

Precision refers to the degree of consistency and repeatability of results obtained from repeated measurements of the same or similar object under specific conditions.

Conducting multiple measurements under the same conditions, if the results are close to each other, then the measurement precision is high. Conversely, the more scattered the measurement results, the lower the measurement precision.

Measurement accuracy

Measurement accuracy, or simply accuracy, describes how close a measured value is to a true value.

If a measurement result are very close to the reference value and exhibit high consistency, it indicates that our measurement accuracy is high; conversely, if the result deviates from the reference value, the accuracy is low.

Accuracy is a qualitative concept that does not have a numerical value and cannot be calculated.

Intermediate measurement precision

Intermediate precision of measurement is the precision of measurement under a set of intermediate precision conditions. Intermediate precision conditions are a set of conditions that may vary over a longer period of time, while using the same measurement procedure, location, and repeated measurement of the same or similar object. The varying conditions may include new calibration and changes in measurement standards, operators, and measurement systems. When reporting the intermediate precision, the conditions should be specified, including the changed and unchanged conditions, as well as the actual degree of change.

Precision and accuracy in 3D scanning

Using the optical 3D measurement system TrackScan-Sharp, Scantech measured a standard gauge block with a length of 1000 mm ten times at a distance of 4.5 m from the i-Tracker, and obtained the following results.

	Nominal (mm)	Actual (mm)	Deviation (mm)
Group 1	1000	1000.025	0.025
Group 2	1000	1000.037	0.037
Group 3	1000	1000.021	0.021
Group 4	1000	1000.039	0.039
Group 5	1000	1000.013	0.013
Group 6	1000	1000.026	0.026
Group 7	1000	1000.025	0.025
Group 8	1000	1000.041	0.041
Group 9	1000	1000.020	0.02
Group 10	1000	1000.031	0.031

According to the official parameters, the equipment has a volumetric accuracy of 0.067 mm when measured at a distance of 4.5 m from the i-Tracker. As shown in the table, all ten measurements meet this requirement, indicating a high measurement trueness. The standard deviation of the ten measurements is 0.0086 and the range is 0.028, which show a good measurement precision.

Conclusion

Trueness, precision, accuracy are crucial aspects of measurement that affect the reliability and significance of the results in various fields. To obtain high-quality measurements, scientists, engineers, and researchers aim to improve all three aspects. By applying appropriate calibration, designing experiments carefully, and choosing suitable measurement methods, we can achieve measurements that are both precise and accurate, which can lead to progress in different areas.

Scantech
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