The longitude of Greenwich has been accepted by international agreement to be the basis from which Longitude would be measured and as such forms the prime meridian for the determination of time. GMT is therefore the exact local time at Greenwich and all other times are expressed as so many hours ahead or behind GMT. (South African Standard time is two hours ahead of GMT).
Iside semeridiyeni samkelwa ngokuvumelana kwehlabathi ukuba ibe sisiseko sokulinganisela iside nto leyo yenza indlela yokufumana ixesha. Ngalo ndlela i-GTM elelona xesha lichanekileyo kwimeridiyeni kwaye zonke ezinye iiyure zichazwa njengeziphambili okanye ezingasemva okanye emva kwe-GTM. (Ixesha elichanekileyo loMzantsi Afrika liziyure ezimbini ngaphimbili kwi-GTM).