GPS satellites

[Forensic]

Hello.

I have a question about a GPS system.

GPS receiver needs minimally three satellites for establishing a position and the fourth satellite is used to correct the clock in the GPS receiver.

Why does the satellite correct the clock after the position has been determined by the three satellites?
I found information that the fourth satellite is used for determining the dimension of height of the GPS receivers position on Earth's surfice.

Which one of these two theories is correct?

Thank you for the answers.

 

[Sammy]

Both are correct. The fourth satellite signal is needed by the GPS receiver to calculate the time taken by GPS signal to reach the GPS satellite to determine the exact location of the object at exact time.GPS tracking system needs 4 signals to exactly locate a position in 3 dimensional.