Precision is an indication of how consistent a measuring device is in a measurement. This may also be used in terms of scientific experimentation as a measure of the experiments reliability. Precision is in contrast to accuracy, which is merely a measure of how close a measurement is to the actual value.
Accuracy and precision are often used interchangeably, although technically this usage is incorrect. As is often the case in experimentation, a measurement may be precise (produce the same value reliably), but it is inaccurate due to a consistent error on the part of the investigator.
At some point, precision reaches a scientific limit. Due to quantum mechanics, and especially the Heisenberg Uncertainty Principle, at some point precision in measurement is impossible without the imparting of energy onto the measured object. For this reason, precision at the atomic level is difficult to obtain. One example is, instead of referring to electrons in a particular location around an atom, scientists determine what area of space they could occupy, and label this area a probability cloud, or an orbital.
In most non-scientific prose, it is common to give approximate values. That being the norm, there is no need to use about in phrases like, "The first airplane was flown by the Wright Brothers 100 years ago."
- Wile, Dr. Jay L. Exploring Creation With Chemistry. Apologia Educational Ministries, Inc. 1998