>>355583883
>I'm not where I want to be right now. I want to be there, not here.
you know where you are at all times
you know this because you know where you aren't by subtracting where you are from where you aren't or where you aren't from where you are whichever is greater 
you obtain a difference or deviation
the guidance subsystem uses deviations to generate corrective commands to drive you from a position where you are to a position where you aren't and arrives at a position where you weren't 
you now are consequently at the position where you are is now the position that you weren't 
You follow that the position that you were is now the position that you aren't in the event that the position that you are in is not the position that you weren't the system has acquired avariation the variation being the difference between where you are and where you weren't 
If variation is considered to be asignificant factor you too may becorrected by the GEA
however you must also know where you were your guidance computer scenario works as follows:
because a variation has modified some of the information you have obtained you are not sure just where you are
however you are sure where you weren't within reason and you know where you were
you now subtracts where you should be from where yoy weren't or vice versa and by differentiating this from the algebraicsum of where you shouldn't be and where you were.