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2. Eden , J. A. 1949a Pin hole stereoplotting instrument Directorate of Colonial Surveys
3. Eden , J. A. 1949b Report on trials with the pin hole plotting instrument Directorate of Colonial Surveys. Unpublished 6
4. A stereoscopic method of photographic surveying;Fourcade;Nature,1902
5. Johns , W. H. 1949 Comments on Mr. Eden's report of the trials with the pin-hole plotting instrument War Office. Unpublished 5