Those errors are the ones that you catch by experience. That means making a comparison with previous done (and well finished) jobs. a When I refer only at theory I feel unsafe for the final result, so I try to search for similar jobs or asks experienced workers. I am sure that experienced workers also in this case of the submarine were complaining that was too heavy. Experienced workers base their "calculations" work on previous done jobs and this is really good to give an idea about if is going to work.