The Aircraft knows where it is at all times. It knows this because it knows where is isn't.By subtracting where it is from where it isn't (whichever is greater) ,It obtains a difference, or deviation. The Inertial Guidence system uses the deviation to generate error signal commands that instruct the aircraft to move from a position where it to a position where it isn't ,arriving at a position where it wasn't or now is. Consequently, the position where it is, is now the position where it wasn,t; thus it follows logically that the position where it is, is now the position where it isn't.In the event that the position where the aircraft position where it wasn't ,the Inertial Guidence System has aquired a variation. Variations are caused by external factors the discussions of which are beyond the scope of this report. Nevertheless the aircraft is sure where it isn't (within reason) and it knows where it was. It now subracts where it should be from where it isn't, where it ought to be form where it wasn't (or vise-versa), and intergrates the differnce with the with the product of where it shouldn't be and where it was; thus obtaining the diffence and it variation, which is a variable constant commonly known as :-lol :-lol :-lolERROR.Andrewfunny stuff form Captain Plummet articals in Aircraft Illustrated magazine

that is exactly how I get home From shopping !Anniette xxxxxxxx

Ah!..... however, I thought that, where ever you go, your always there... so maybe I'm aren't.... so your saying that you are where you are going and wisn't where you are now... ?That would explain a lot.Thanks for clearing that up:-)Pete