The missile knows where it is, you see,
By knowing where it ought to be.
It tracks where it is and where it’s not,
Subtracting one from the other on the spot.
By finding the difference, a deviation it finds,
Corrective commands are issued in kind.
To steer the missile from here to there,
From a place it isn’t, to one that’s fair.
When it gets to a spot where it wasn’t before,
It realizes it isn’t there anymore.
The position it was, it now can’t be,
For now it’s somewhere else, you see.
If the place it’s in isn’t where it wasn’t,
It figures out the variation present.
The guidance system corrects the drift,
To align the path and give it a lift.
Though the missile’s unsure where it might be,
It knows where it isn’t, quite clearly.
By calculating both error and variation,
It adjusts its path with great elation.
Thus, the missile stays on its flight,
Correcting its course both day and night.
Through subtracting, adding, and knowing its place,
It stays on target, keeping pace.