The dip sector consists of a varnished brass frame and index arm. The index arm carries the glass, without adjustment, and is moved by hand. The sight vane with a narrow slit parallel to the horizon is fixed to the frame, but the glass can be set by hand and secured with a milled clamping screw on the back of the frame. 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 moving the index arm and the dip or rising of the horizon is read from the scale along the indicating line.

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