Standard time
In 1870 Charles F. Dowd proposed four time zones based on the meridian through Washington, DC for North American railroads. In 1872 he revised his proposal to base it on the Greenwich meridian. Sandford Fleming, a Scottish-born engineer operating in Canada, proposed worldwide Standard Time at a meeting of the Royal Canadian Institute on February 8, 1879. Cleveland Abbe advocated standard time to better coordinate international weather observations and resultant weather forecasts, which had been coordinated using local solar time. In 1879 he recommended four time zones across the contiguous United States, based upon Greenwich Mean Time. The General Time Convention (renamed the American Railway Association in 1891), an organization of US railroads charged with coordinating schedules and operating standards, became increasingly concerned that if the US government adopted a standard time scheme it would be disadvantageous to its member railroads. William F. Allen, the Convention secretary, argued that North American railroads should adopt a five-zone standard, similar to the one in use today, to avoid government action. On October 11, 1883, the heads of the major railroads met in Chicago at the Grand Pacific Hotel and agreed to adopt Allen's proposed system.
North American Numbering Plan expansion
The North American Numbering Plan was devised in the 1940s, implemented in 1947, and has provided customer direct-dialed long-distance telephone service since 1951. Occasionally, the growing demand for telephone numbers has mandated certain changes in the format of telephone numbers and method by which they are allocated to telephone companies. Instead of expanding the size of telephone numbers, as implemented in many countries outside North America, the NANP was designed as a closed numbering plan, having a fixed number of digits, three digits for the numbering plan area (NPA) code and seven digits for telephone numbers that are unique in each NPA. The telephone number was further distinguished as consisting of three digits that identified each central office and four digits for each subscriber station connected to the same central office. From 1947 to c. 1960, the initial two digits of the central office code were mapped to two letters of an often locally significant name, the central office name or exchange name. However, this scheme, practiced since its invention by W. G. Blauvelt of AT&T in 1917, prevented the use of numerous digit combinations that could only be associated with unpronounceable or, at best, confusable names. All-number calling removed these restrictions and permitted the phasing out of exchange names. Central office codes were initially still restricted from using digits "0" and "1" in the middle position, which provided a distinction to area codes, which always had "0" or "1" in the middle position. This last restriction was removed by 1995, with the phase-out of electromechanical switching systems by programmable electronic switching systems (ESS).