INERTIAL GUIDANCE SYSTEM SIMPLIFIED

Not sure who the author of the following article is, however, the
article is one of the best, clearly defined descriptions of the magic
that resides within the aircraft's black boxes.

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The aircraft 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 the greater), it
obtains a difference, or deviation.

The Inertial Guidance System uses deviations to generate error signal
commands that instruct the aircraft 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 the aircraft now is, is not the
position where it wasn't, the Inertial Guidance 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 the aircraft is and where
the aircraft wasn't. If the variation is considered to be a factor of
significant magnitude, a correction may be applied by the use of the
autopilot system. However, use of this correction requires that the
aircraft now know where it was because the variation has modified some
of the information that the aircraft has, so it is sure where it isn't.


Nevertheless, the aircraft is sure where it isn't (within reason) and
it knows where it was. It now subtracts where it should be from where
it isn't, where it ought to be from where it wasn't (or vice versa) and
integrates the difference with the product of where it shouldn't be and
where it was; thus obtaining the difference between its deviation and
its variation, which is variable constant called "error".