This analysis assumes the stress is evenly distributed over the entire cross-section. In practice, depending on how the bar is attached at the ends and how it was manufactured, this assumption may not be valid. In that case, the value formula_3 = "F"/"A" will be only the average stress, called "engineering stress" or "nominal stress". However, if the bar's length "L" is many times its diameter "D", and it has no gross defects or built-in stress, then the stress can be assumed to be uniformly distributed over any cross-section that is more than a few times "D" from both ends. (This observation is known as the Saint-Venant's principle).