Budipro
****'s excellent and comprehensive reply will go far to solving those DR conundrums in the air that all airborne pro's occaisionally suffer from, especially our elite front line pilots that police the skies of the world so that you and I can sleep soundly.
Most, if not all of our modern high tech fighter aircraft use complex high tech navigational systems like Decca. Because **** is a serving member of the RAF he is not at liberty to disclose this name, merely refering to it as 'the system'. I am not a serving member therefore I am and this has been approved by Claire Short.
The complex algorithms are based on the mathematical probabilities of where the aircraft may be as opposed to where it wasn't or where it should be assuming of course that the air plot was based on a position where the aircraft could be. This mathematical formula is know as Sodanos Confluence and makes heavy use of the principal of latitudinal and longtitudanal convergenge and the influence of temperature deviation with latitude on the boiling point of angles, ie a right angle at 90N will boil at 100 Degs C whereas at the equator it's more like 104.32 C.
Another rule that comes in handy is the 1 in 60 rule, this means that for every 60 nms or 60 degs off course you are you only have 1 chance to correct it (especially at low level in mountainous terrain, CFIT etc etc)
Good luck