A reference to an historical navigation method.  Starting from a place of certainty by calculating a previously determined position and then advancing that position with the use of instruments and analysis. The process of dead reckoning allows the navigator to know where they are in a featureless ocean.  However, sometimes ships are knocked off course by un-foreseen natural events and are lost.

steel balloon suspended, mid air, by a magnetic field

 

balloon field, one of several iron balloons suspended by an invisible magnetic field.