Distinguish Between Accuracy & Precision Measurement - SKENGINEERS India

 Distinguish Between Accuracy & Precision Measurement.

When defining a project scope, its essential to have Accuracy & Precision.

What's the difference between accuracy and precision?

ACCURACY:-

It is defined as, "the closeness of measured value of component produced with its true value".

PRECISION:-

Precision is the repeatability of  measuring process. It shows 'how well identically performed measurements agree with each other'.

DIFFERENCE

ACCURACY	PRECISION
1.Accuracy is the agreement of measured value with the true value of measured quantity.	1.Precision is the repeatability of measuring process. It shows how well identically performed measurements agree with each other.
2.Accuracy is concerned with true value.	2.precision is concerned with mean value . precision has no concern with true .precision has no meaning for only one measurement. But exist only when number of measurement are carried out for measuring same quantity under identical conditions.
3.If true value is 10mm, then 9.99mm is more accurate than 9.91mm.	3.If true value is 10mm, and readings obtained are 10.001, 10.002, 10.003, 10.004, 10.005 mm, then mean value of reading will be 10.003mm.
4.It is difficult and expensive to have good accuracy.	4.It is much and cheaper to achieve great accuracy.
5.High accuracy cannot be obtained with low precision.	5.High precision can be obtained with low accuracy.

• FACTORS AFFECTING THE ACCURACY

1. Calibration standards :- 

Accuracy may affected by ambient (atmosphere) conditions, such as, expansion of metal used in measuring instruments due to rise in temperature, elastic properties of metals and stability of instruments over a long period.

2. Workpiece being measured :-

Accuracy may be affected by the condition of workplace such as, cleanliness , surface condition, proper arrangement etc.

3. Measuring instruments :- 

Measuring instrument and hence accuracy may be affected by sources of errors such as, hysteresis, backlash, friction, zero drift error, deformation in handling or use of heavy workpieces.

4. Human Error :-

The person or inspector carrying out the measurement may not have the required skill. improper training or lack of handling skill or casual attitude of inspector may affect the measured value and hence accuracy.

5. Environment Influences :-

Changes in atmospheric  (ambient) conditions such as temperature, vibrations, lightening, pressure etc. may affect the accuracy.