The paper entitled The Photogrammetric Society Analogue Instrument Project was published in The Photogrammetric Record 14(82): 565‐582 (October 1993). Extracts have appeared in each subsequent issue such that all the standard types of analogue instruments mentioned in the catalogue have now been included, some 28 instruments in all.In this final extract, the three remaining instruments listed in the catalogue are dealt with. All are of a type usually known as approximate solution instruments because they did not attempt any form of accurate space intersection but relied on applying a number of corrections to a model formed on the assumption that the photographs being used were true verticals taken at the same altitude. The accuracies achieved by such instruments depended both on how close the photography being used was to this ideal situation and on the degree of sophistication in the design of the analogue correctors incorporated in any particular instrument. The raison d'être for such a genre of instrument was essentially one of cost. Any organization faced with the requirement to produce small scale topographic mapping of an extensive region within a reasonable period of time might consider spending its available funds on a larger number of cheaper approximate solution instruments, always provided that an acceptable degree of accuracy could be maintained. Fortunately for such projects the specification would normally be for mapping of a graphical order of accuracy produced from high altitude photography. At such altitudes, stable flying conditions and small camera tilts of the order of 3° to 4° could realistically be expected. However, to obtain the best possible results from such photography, the best images possible should be provided for the operator, a factor sometimes overlooked by some manufacturers in their attempts to produce cheaper instruments.In view of the background to the development of British photogrammetry mentioned in previous extracts, it is perhaps surprising that a successful instrument of this type was not produced in the UK at a much earlier point in the era of analogue photogrammetry. Approximate methods were certainly favoured and promoted but only as far as planimetric maps were concerned. For these, form lines rather than contours were drawn when height information was considered necessary. However, when it was finally produced, the Thompson CP1 (manufactured by Cartographic Engineering Ltd.) proved to be an excellent instrument of its type and less approximate in its solution than most of its competitors. The other two instruments described in this extract are the Zeiss Stereotope and the Galileo‐Santoni Stereomicrometer. The instruments are introduced in the order of their appearance on the market, which is also the order of the degree of sophistication found in the analogue computers they employed to reduce the errors introduced by any camera and airbase tilt present in the photography.