r recording, being tested in products and voted on by form specialist functions and are exclusively separate transmit and the users. receive units, for transmission in one direction. Document facsimile Throughout these equipment designs a continuous compromise types are almost exclusively transceivers. was necessary concerning resolution and transmission time. The Table 60.1 summarises the characteristics of the different types of results had to be good but not too good because speed was always facsimile equipment. of the essence. Facsimile development, like all communication evolutions, wanted higher bandwidth on existing circuits or faster circuits at the 60.2.1 Photofax equipment same cost. It may not be too high a claim to make that facsimile developments have pressed network use to its highest efficiency, It is used for the transmission of full tone photographs of size often exceeding the expectations of the network providers. normally less than A4. Often the received picture is printed on The development of weather map transmission equipment from photographic paper. The important requirements are not image size the mid 1940s allowed meteorologists access to International charts, but correct aspect ratio, which is preserved by using the same index compiled in National Centres, so they could make their own local of co-operation. forecasts. A clear case for the immediate distribution of information Some scanners are designed to transmit colour separations from in the format preferred by the user. Yesterday's weather forecast is 35mm colour negatives using sequential transmission. Photofax not of much value. equipment may be used, one transmitter to one receiver for example In the mid 1950s page facsimile units for the transmission of for sending news photographs from field locations, or one transmit- whole newspaper pages started to become available. These large ter broadcasting on a wirephoto distribution network to many re- format machines, with high resolution to preserve the half tone dot ceivers. The tran