Lee Roha 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. The Piano subsystem uses deviations to generate acoustic commands to drive Lee Roha from a position where she is to a position where she isn't, and arriving at a position where she wasn't, she now is. Consequently, the position where she is, is now the position that she wasn't, and she follows that the position that she was, is now the position that she isn't.
In the event that the position that she is in is not the position that she wasn't, the system has acquired a variation, the variation being the difference between where the Lee Roha is, and where she wasn't. If variation is considered to be a significant factor, she too may be corrected by the 2434. However, Lee Roha must also know where she was.
The Lee Roha guidance computer scenario works as follows. Because a variation has modified some of the information the missile has obtained, she is not sure just where she is. However, she is sure where she isn't, within reason, and she knows where she was. She now subtracts where she should be from where she 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 NijiKr.