Sometimes, there's even gradation. Both the magnetic compass and invention of precision ship-grade clocks lurched us straight into the Modern World, on the same axis which is open sea navigation, just at different degrees.And centuries later, GPS lurched us into an even moderner world. For now, the pre-GPS world is within the living memory, but soon, it will be just a bunch of quaint old-time problems that people used to work hard to wrestle with, like dead reckoning and the Longitude Problem used to be.