In Greenwich, the magnetic field of Earth is 8.5 degrees, whereas in Mecca the magnetic field is zero.
It has been proven that there is a certain discrepancy if we calculate it according to Greenwich. This discrepancy has been estimated as 8.5 minutes between the northern and southern hemispheres.
It will make air traffic safer.
Basing time on GMT prevents people who live very near the poles from visiting Mecca.