In the episode The Stolen Earth, the doctor and Donna Noble followed the Tandocca Scale to where it went off : Medusa Cascade. Then they had no clue about the stolen planet until the doctor was called by the signal from Earth. And finally the Doctor concluded that the Medusa Cascade have 1 second out of sync with the rest of the universe and this was why they couldn't find the stolen planets. Then the doctor locked on to the signal and BAM! - the Tardis went to the correct path and they found themselves in the middle of the stolen planets.
I really don't understand the concept of 1 second out of sync. Could someone explain it please?