Linked from
The 14 pages that link to Greenwich Mean Time, each with the reason it gives.
Marine chronometerRelated: A ship compared its chronometer’s Greenwich time with local solar time.
Time zoneRelated: It became the reference from which many early zone offsets were measured.
Pendulum clockRelated: Accurate observatory clocks helped establish and distribute standard time.
Solar timeRelated: It exemplifies a standardized time anchored to mean solar time at one longitude.
Railway timeRelated: British railways adopted it in place of varying local times.