What factors influence the precision of measuring tools?

Answer 1

A Discussion about Precision and Accuracy Precision and accuracy are two terms used interchangeably by the general population. The precision of a measurement is determined by how reproducible that measurement value is. The accuracy of a measurement is the measure of how the answer compared to reality. You need both to have a true measurement.

Precision: For example, if a sample is weighed by a student to be 42.58 g, and then measured by another student five different times with the resulting data:

Data: 42.09 g 42.15 g 42.10 g42.16 g 42.12 g No comment can be made about the accuracy of the measurements as the actual value is not known. The second student's values however only range between 42.09 and 42. 15 grams giving a variation of only 0.2% between the high and low observed values. The first student would exhibit good precision but still be wrong because his data set is not accurate. As to what makes a device precise: * It should be sturdy so that components are not twisted out of alignment * It should be constructed to standards and tolerances that are known and can be monitored

* It should be stable in a wide range of temperature and humidity or capable of maintaining known temperatures and humidity * It should be accompanied by a QA/QC and PM program

Accuracy:

The accuracy of a measurement is determined by how close a measured value is to its "true" value.For example, if a sample is known to weigh 3.182 g, and then weighed five different times by a student with the resulting data:

Data: 3.200 g 3.180 g 3.152 g3.168 g 3.189 g

Then the most accurate measurement would be 3.180 g, because it is closest to the "true" weight of the sample. The precision of the data is another issue. The values range between 3.152 g and 3.200 g. a range of .05 g or almost 2% difference between the high and the low. The second student is not precise but has stumbled across an almost correct answer. He is in no position to know which of his answers is correct.

As to what makes a device Accurate: * It should have internal or external standards for zeroing and full range measurement * It should be part of periodic QA/QC programs for Accuracy * It should meet the criteria for Precision

Non-Laboratory Examples:

If a carpenter built a house with a non-Accurate tape measure every room would be square and by his tape the exact right size. He would be precise. However, when it came to install a 4' x 8' rug in his 4' x 8' room it would not fit as he was not accurate.

If a cook has an oven that has a bad temperature control, it is not precise. If he wants to cook cakes at 375o F for one hour. The cakes will be burnt sometime and underdone at others

Answer 2

Human error, manufacturing differences in measurements.