What many don't realize about OR's Herbie system - some deep background
Herbie's Automatic Inertial Guidance System
Herbie automatically knows where he is at all times. He knows this because he knows where he isn't. By subtracting where he is from where he isn't, or where he isn't from where he is (whichever is the greater), Herbie obtains a difference, or deviation.
His Inertial Reference System uses deviations to generate error signal commands which instruct USA 17 to move from a position where it is 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 was is the position where it isn't. In the event that the position where USA 17 now is, is not the position where it wasn't, Herbie's Inertial Reference System has acquired a variation. Variations are caused by external factors, the discussions of which are beyond the scope of this report.
A variation is the difference between where USA 17 is and where the boat wasn't. If the variation is considered to be a factor of significant magnitude, a correction may be applied by Herbie, through the use of His autopilot system. However, use of this correction requires that USA 17 now knows where it was because the variation has modified some of the information which USA 17 has, so Herbie is sure where the boat isn't.
Nevertheless, Herbie is sure where USA 17 isn't (within reason) and it knows where it was. He now subtracts where it should be from where it isn't, where he ought to be from where the boat wasn't (or vice versa) and integrates the difference with the product of where he shouldn't be and where the boat was; thus obtaining the difference between its deviation and its variation, which is variable constant called "error".
This is one of the few spy photos of an actual " herbie " .
Some people mistakenly assumed it to be a flux capacitor