Most pre-grouping railway companies had their own styles of signal box, with a number of standard styles also available from the main contractors for the supply of signalling equipment. The standard work of reference on signal box style, The Signal Box, lists three different styles of box built by the Great North of Scotland Railway. It also lists a fourth design, by the Railway Signalling Company, of which the box at Kennethmont is the only survivor. Study of photographs of GNS confirms this basic classification but identifies sub-divisions for two of the types. These have been added to the original classification with the agreement of the author of The Signal Box. To summarise, the original classification of the designs was :- Type 1 was a hipped roof design with STF (stone/brick to floor) and vertical boarding above. Type 2 was a very much plainer design that the others. It had a gable roof and all wooden construction with horizontal boarding. Type 3 was a hipped roof, all wooden construction box, again with horizontal boarding. There was more ornamentation on this box than on the type 2 design. Railway Signalling Company hipped roof. The Great North built at least 160 signal boxes, of which about 130 appear on known photographs. Fifteen of these do not fall in any definable category, but analysis of the remainder shows that types 2 and 3 in the above classification should each be split into two sub-types. It has also been possible to date nearly all the boxes from the Weekly Circulars published by the GNSR, since a complete series of these has survived from 1887, mainly in the Scottish Record Office. Board of Trade Inspection Reports have provided correlation of these dates, together with some earlier opening dates. Cross-referencing the designs to the building dates shows a chronological pattern to the introduction of the designs with only a few anomalies, for which explanations can only be surmised. Sometimes what is described as a ‘new signal box’ must have really meant refurbishing an old one but it is known that the Great North moved boxes around the system. There are five examples of type 1 which date from the time that type 2 boxes were being built in large numbers. Given that they have substantial stone bases, it is difficult to assume that they were moved from elsewhere, but no other explanation is obvious. Most lines on the Great North were built before 1866 and therefore the signalling provided was rudimentary, with points operated from the ground next to them. There was no interlocking of points and signals and therefore little need of signal boxes. By the time the Coast line from Portsoy to Elgin was opened, between 1884 and 1886, interlocking was a requirement of new lines and was provided from the start. The main line was doubled from Dyce to Inveramsay in 1880, so must have been properly signalled from then. Most boxes on the rest of the system were built in the period from 1890, when interlocking was applied throughout the system in conformance with the Regulation of Railways Act, 1889, the Great North being among the last companies to fully comply with that legislation. At single line crossing places, two signal boxes were generally required because of the length of point rodding required at the loops, a main one near one end of the loop which would also control the sidings and contained the block instruments, and a minor one at the other end. Great North practice differed from the Highland who placed the block instruments in the booking office, with levers there to control slots in the starting signals. In most case, both boxes were of the same design but there are examples where different designs were used. Where the same design was used, standardisation was followed in some cases to the extent of equipping a fireplace in the minor box, even though the signalman could only have been there for a few minutes each day! GNSRA has published a DVD with signalling diagrams for the majority of GNSR signal boxes.