Series IV. Ledgers, 1916-1993, contains 42 boxes, totaling 45.02 cu. ft. It primarily consists of survey record books (not field notebooks). Many record "Survey By", "Traverse by", Notebook No., Page No., Station, Azimuth, Reduced Vernier, Cosine, Horizontal Distances, Sine, Latitude (North and South), Departure (East and West), Sums of Latitude (N&S) and of Departure (E&W), Remarks. N.B.: TT looks like pi sometimes.