Onceapilot, if it goes wrong, most of us have iPhones. With built in GPS.
Not to mention most aircraft having one, two or even 4 independent ring l@ser gyros, updatable with GPS, radar or nav aid fixing.
In flight, perhaps. The discussion is actually about
pre-flight planning! I contend that, for speeds of less than about 210 KIAS, MDR is insufficiently accurate when either a whizz-wheel, nav calculator or software can provide an accurate answer in next to no time.