DescriptionTopographic Abney Level, model 5713PD, made by Keuffel & Esser Co., (New York), no date, circa 1950-1960. Metal and glass; level tube with black cloth finish, 11/16" square x 6-3/8" long; extends to 7-3/16 open; stainless steel graduated arc circa 4" long x 2-1/2" high; attached glass bubble with brass and steel mount with partial black cloth finish; lens eyepiece. With: sewn tan leather case with belt loop; original two-piece cardboard box with printed label on end. Accompanied by instruction manual, K&E Manual; Abney Levels, copyright 1950. This item is separately catalogued as archives 2009.006.0153.01 The model name and number does not appear on the object. "Keuffel & Esser Co." is on the "Percent" side of the arc. This model of the Abney level was an improved version made for the U.S. Forest Service. It had been described as such since the 1920s. A description is on page 394 of 42nd edition catalog, 1954. The arc is graduated on both sides: "Percent", in percent of grade (seen to the outside or left side); "Degrees", in single degrees on the other (right side) which in order to use it, it has to be dismounted and turned around. This procedure is discussed in the instruction manual. K&E had their main office and factories in Hoboken when this item was made.