Software validation

You may think of a PKPD software as a calculator. You expect that operations in a calculator are correctly performed internally, so that the machine returns the correct answer. However, as a calculator, the answer is only accurate if it is correctly operated, and the problem at hand is correctly translated into sequential operations that give the correct answer. For instance, how many seconds are there in a day? The correct answer is 246060=86400, and not 24+60+60=144. A validated calculator will give both answers, 86400 and 144 (and not any other number), depending on how it is operated. The result is only as good as the ability of the calculator operator to translate a real-world problem into a tractable mathematical problem that correctly approximates reality (> Essentially, all models are wrong, but some are useful> (George Box, a famous statistician)).

https://www.certara.com/2011/03/08/software-validation-do-i-have-to-do-it/