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.A triangulation diagram appears on the reverse of this drawing. This enabled the draughtsman to plot features of the landscape with precision.,A trigonometrical point is marked at Air Lighthouse at the top of the plan. Pencil lines radiate from this point, indicating the angular measurements taken from here. Archaeological sites are,labelled,in gothic script. ,'Tumuli' (ceremonial burial mounds) are marked in this way in several places.
Durrant, William R