The dip sector consists of a varnished brass frame and index arm. The index arm carries the glass, without adjustment, and is moved by a milled tangent screw. A second milled tangent screw moves the sight vane, which is missing. The screw on the back of the pivot, which secures the glass mount, is missing. Through the sight vane the observer looks toward the horizon and at the same instant sees the reflection of the horizon behind him in the glass, at an angle of 180 degrees. The two horizons are brought in line by the tangent screw moving the index arm, and the dip or rising of the horizon is read from the scale along an indicating line.

The instrument has a varnished brass scale measuring by 0.5 arcminutes with no digits.