It marks the site of the old Grand Pacific Hotel where the General Time Convention of 1883 met and "adopted the current Standard Time System in the United States. The convention was called by the railroad industry to develop a better and more uniform time system to govern railroad operations. Previously, time had been determined by the position of the sun with high noon as the only existing standard of exact local time. More thatn 100 different local times resulted from this method."
The Standard Time System set up the four time zones all railroad clocks in each zone were synchronized to strike the hour simultaneously. The system was inaugurated on November 18, 1883. On that Sunday the Alleghany Observatory at the University of Pittsburgh telegraphed when it was exactly noon at the 90th meridian. Railroad clocks across the nation were then all reset on the hour according to the time zone thy were in.
The Federal Government adopted the system immediately but Congress did not enact the Standard Time Act until March 19, 1918.