Precision

Precision is an indication of how good the measuring device was in a measurement.

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."