Mannnny mannny years ago whilst doing a DR Nav the co, way before GPS etc pulled out a calculator with what he had set up to calculate PNR, SFC etc ( now is probably known as an app). When the initial query of what he was doing was explained about his wiz bang calculator and therefore why he was not using the whizz wheel my next question of what would happen when his battery ran out was met with a slightly contemptuous look. He then pulled out of his bag a fist full of batteries. Not to be put in my place I than asked what would happen if the almighty calculator blew a tube. After receiving a further contemptuous look to put me back in place he pulled out another calculator. The basic art of DR mental or NAV was being replaced by technology and no longer required the back up of the operator learning/knowing the art of manual calculation.