Corrected that to make D-R fit!!!Some navigators joke that the derivation of this phrase comes from “Dead Rong,” referencing the unreliability of this technique. Others suggest it is a derivative of “deduced reckoning,” arguing that historical records sometimes refer to it as “ded. reckoning.” Research into the origins of the phrase does not support either of these claims, although the term itself dates to at least the 1600s, when it began to be used by English navigators.
If it's so unreliable how come it works!!!!