Note, Podge and John et al, will already know this in one form or another.
This text was originally transcribed from a US Navy training film.
Aircraft Inertial Guidance Systems
The aircraft knows where it is at all times. It knows this because it
knows where it isn't, or wasn't. By subtracting where it is from where it isn't, or wasn'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 which instruct the aircraft to move from a position where it
is to a position where it isn't, or wasn't arriving at a position where it
wasn't, or now is, or isn't. 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, or possibly wasn'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, or was it isn'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 knows where it was because the variation has modified
some of the information which the aircraft has, so it is sure where it
isn't, or wasn'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
Then I started the real lecture... and they thought the above was perfectly simple in comparison