Further original documents written by Agas survive among the Lansdowne and Additional manuscripts in the British Library. One is a letter dated 22 February 1593, addressed to Lord Burghley. It is entitled "A Noate for the Perfection of Lande Measure, and exact Plattinge of Cities, Castels, Honors, Lordshippes, Maners, and Landes of all sortes". In this account of the techniques of land-surveying, Agas writes of the "profitable staff" and the theodolite of some 20 inches in diameter, with a protractor of one foot at least. He adds that "the measure attendinge uppon this instrument is of steele wier toe pole longe lincked foote by foote, excepte the halfe foot at either ende." In another letter to Burghley of 1597, Agas writes of his labours in the Fens of eastern England, and states how he had plotted out the ground, gauged the quantity of the waters, the ebbs and flows, and the daily abuses of the landholders. He thanks Burghley for bounties already bestowed, but also alludes to a considerable sum still owing to him for his services.