Thought this might be a lark. · 4:05pm April 2nd
Rainbow Dash knows where she is at all times. She knows this because she knows where she isn't. By subtracting where she is from where she isn't, or where she isn't from where she is (whichever is greater), she obtains a difference, or deviation. He internal sense of direction uses deviations to generate corrective commands to drive the Pegasus from a position where she is to a position where she isn't, and arriving at a position where she wasn't, it now is. Consequently, the position where she is, is now the position that she wasn't, and it follows that the position that she was, is now the position that she isn't.
In the event that the position that she in is not the position that it wasn't, the system has acquired a variation, the variation being the difference between where the feather-horse is, and where she wasn't. If variation is considered to be a significant factor, it too may be corrected by the ISOD. However, Rainbow Dash must also know where she was.
The Pegasus navigation scenario works as follows. Because a variation has modified some of the information the Pegasus has obtained, she is not sure just where she is. However, she is sure where it isn't, within reason, and she knows where it was. It now subtracts where she should be from where it wasn't, or vice-versa, and by differentiating this from the algebraic sum of where she shouldn't be, and where she was, she is able to obtain the deviation and its variation, which is called error.
Fascinating creature