A train order is "an order issued by or through a proper railway official to govern the movement of trains". Train order operation is the system by which trains are safely moved by train orders. It is distinguished from other forms of train operation in which the authority to move trains is given by fixed signals or Cab signalling. Train order operation, or more accurately timetable and train order operation, was the standard operational system used by the railroads of North America before the days of centralized traffic control, direct traffic control, and the use of track warrants conveyed by radio. The system used a set of rules when direct communication between train dispatchers and trains was limited or non-existent. Trains would follow a predetermined operating plan, known as the timetable, unless superseded by train orders conveyed to the train from the dispatcher, through local intermediaries. Train order operation was a system that required minimum human overhead in an era before widespread use of technology-based automation. It was the most practical way for railroads with limited capital resources, or lines with limited traffic, to operate. To this day, many short lines, heritage railways, and railroad museums continue to use Train Order operation. The process of modernization in the 19th century was a transition from a spatially-oriented world to a time-oriented world. Exact time was essential, and everyone had to know the exact time, resulting in clock towers for railway stations, clocks in public places, and pocket watches for railway workers and travelers. Trains departed on time (they never left early). By contrast, in the premodern era, passenger ships left when the captain had enough passengers. In the premodern era, local time was set at noon, when the sun was at its highest. Every place east to west had a different time and that changed with the introduction of standard time zones. Printed time tables were a convenience for travelers. More elaborate time tables, called train orders, were essential for train crews, maintenance workers, station personnel, and repair and maintenance crews, who knew when to expect a train. Most routes were single track, with sidings and signals to allow lower priority trains to be sidetracked. Schedules told everyone what to do, where to be, and exactly when. If bad weather disrupted the system, telegraphers relayed immediate corrections and updates throughout the system. Just as railways as business organizations created the standards