Where are you?

(Verse 1) The missile 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 (Chorus) It obtains a difference, or deviation The guidance subsystem uses deviations To generate corrective commands Drive the missile from a position where it is To a position where it isn't (Verse 2) Arriving at a position where it wasn't Now it is, consequently The position where it is, is now the position That it wasn't, and it follows That the position that it was Is now the position that it isn't (Chorus) In the event that the position that it is in Is not the position that it wasn't The system has acquired a variation The variation being the difference Between where the missile is And where it wasn't (Bridge) If variation is considered to be a significant factor It too may be corrected by the GEA However, the missile must also know Where it was (Verse 3) The missile guidance computer scenario Works as follows because a variation Has modified some of the information The missile has obtained, it is not sure Just where it is, however, it is sure Where it isn't, within reason And it knows where it was (Chorus) It now subtracts where it should