The missile knows where it is at all times. He knows it because he knows where he is not. By subtracting where it is from where it is not, or where it is not, where it is (whichever is greater), you get a difference or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the missile from a position where it is to a position where it is not, and reaching a position where it was not, now it is. Consequently, the position where it is now is the position that it was not, and it follows that the position that it was now is the position that it is not. In the event that the position you are in is not the position you were not in, the system has acquired a variation. Variation is the difference between where the missile is and where it is not. If the variance is considered a significant factor, the GEA can correct it, however the missile must also know where it was. The missile guidance computer scenario works as follows: because the variation has modified some of the information the missile has obtained, you are not sure where it is, however you are sure where it is not, inside reasonable, and you know where it is. It was. Now subtract where it should be from where it was not or vice versa, and by differentiating this from the algebraic sum of where it should not be and where it was, it is able to obtain the deviation and its variation, which is called "error.”