“Accuracy” and “precision” are related but not identical concepts, and the difference between the two is important to estimation. Accuracy of a measurement system is the degree of closeness of measurements of a quantity to its actual (true) value. The precision of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results.
Let us understand this with an example, ‘1 yard = 91.43999 cms’. Accuracy refers to the ‘correctness’ of a measurement i.e 91 cms is a more accurate representation of 1 yard while precision could be identified as the ability to resolve smaller differences i.e. 91.44 cms is a more precise representation of 1 yard.
A measurement can be precise without being accurate, and it can be accurate without being precise. 91 cms is an accurate representation of one yard, but it is not precise. 91.3333 is as precise representation of 1 yard, but it is not accurate. Airline schedules, train timings are usually precise to the minute, but they are not very accurate. Measuring people’s height in whole feet might be accurate, but it would not be precise.
For example, suppose one employee estimates that the a particular project will be completed in 2 and 6 days but he actually completes the project in 5 days. Thus, the estimation is accurate, but not very precise. However, second employee estimates that the project will be completed in 6 days but takes 8 days to complete it. This estimation by second employee is very precise, but completely inaccurate.
Shortest possible execution is achieved by creating the most accurate estimates possible, not the most precise. If you want to achieve fastest execution, avoid false precision.