Please read the first few paragraphs of Chapter 1 from
this paper
from this page
http://www-personal.engin.umich.edu/...b/position.htm
The author gives a very good description of dead reckoning.
It is also a nice reference for all the different types of autonomous movement. Let me warn that it is rather long, and at times mathematically complex. It is also somewhat outdated (written in 1996), but most of the concepts still hold true.