The six digit National grid References of the marked positions on the 1824 map are taken from an equivalent modern map. The four digit references are much less accurate, being taken from an Ordnance Survey map by inspection of Wright Fig.3. The Ordnance Survey does not note the Friars Bar toll gate but in the Exeter Estate book, the position is called Friers Bar though no obstruction of the road by a gate is indicated. "Paterson's Roads" is a road book listing the features of roads and mileages from the ends of its itineraries, sequentially.