Dead reckoning
It is used to track where a ship or airplane or sometimes where a vehicle on land is at.  Now, Global Positioning System (GPS) is used and dead reckoning is not as important.  But it is still used in areas where GPS is not available or for short periods of time if a GPS update is missed.  It is also good to know in case the GPS satellites are damaged by a solar flare, or equipment is lost or broken, so it is still taught to sailors and pilots.