There are approximately 54,000 subscribers to TWX at this writing, and the TWX directory gets fatter with each new issue. In 1962 all TWX machines were converted to direct dialing operation, making the service easier to use. Instead of going through “Operator” by manually typing out the call letters of the party being called, one now merely depresses the Originate button, listens for the dial tone, and then dials the TWX number of the party wanted. RCA Communications, Inc., was the first to extend international TELEX service to Bell System teletypewriter subscribers (1955), enabling them to make and receive overseas calls on their domestic TWX machines.[14] As stated, the TWX machines were geared for 60-words-per-minute operation, whereas the TELEX system operated at 66 words per minute. It was therefore necessary for R.C.A. to use conversion apparatus to an error-detecting code for overseas radio transmission. This code was a seven-unit code, using three marking and four spacing elements, giving 35 usable combinations. By using a special printer, when a faulty combination was received, a special error symbol was printed. Western Union, in May of 1958, introduced TELEX service between New York City and various Canadian points. By 1962 the service had been extended to 67 United States cities, and at this writing they expect to serve 180 United States cities with an anticipated subscriber capacity of many thousands.[15] In addition to domestic service between U. S. cities, subscribers can dial automatic teleprinter connections to Canada and Mexico. Also, they can obtain direct TELEX connections to other parts of the world through the overseas facilities of RCAC (Radio Corporation of America Communications), AC&R (American Cable and Radio), and WUI (Western Union International). The operating speed of 66 words per minute and also the teleprinter keyboard in the U. S. TELEX network conform to international standards of the CCITT. This provides complete operating compatibility with other TELEX systems throughout the world without the need for speed and keyboard translators.[15] SOME OF TODAY’S TELEX APPARATUS [Illustration: The SAGEM Electronic Teleprinter used in TELEX _Picture by courtesy of Société d’Applications Générales d’Electricité et de Mécanique_] [Illustration: Western Union TELEX _Picture through courtesy of Western Union Telegraph Co._] [Illustration: General Post Office TELEX Installation _by courtesy of H. M. Postmaster-General_] [Illustration: (uncaptioned)] [Illustration: Standard Elektrik Lorenz TELEX Apparatus _reproduced by permission of Standard Elektrik Lorenz_] [Illustration: Siemens & Halske TELEX Apparatus _Picture by courtesy of Siemens & Halske_]