The Definition of the Inertial Guidance System

As explained by Coach John Hutchison,
Chemistry/Physics Teacher emeritus

The inertial guidance system knows where it is at all times.  It knows this because it knows where it isn’t.  By subtracting where it is from where it isn’t or where it isn’t from where it is, whichever is greater, it obtains a difference or deviation. 

The Inertial Guidance System is the deviation to generate corrective commands to drive the aircraft from the position where it is to a position to where it wasn’t.  It is now consequently where it wasn’t at a position to where it was if the position is where it isn’t. 

The thought process of the inertial computer is as follows:  Let us assume that the system is not sure where it is, however, it is sure where it isn’t.  Within reason, and it knows where it was, it now subtracts where it should be from where it wasn’t, whereby or vice versa, and by differentiating this from the algebraic difference between where it shouldn’t be and where it was, it is able to obtain the difference between its deviation and variation and is thus able to obtain its present position.