This device is housed in a wooden case with wedges and a sliding console. It also contains a cord, at the end of which is fixed a conical metallic weight and a marker consisting of a disc and a rod. These two elements are attached to a tripod. The marker is set at one of the apexes of the triangle defined for the measurement. The plumb line is attached to the tripod flange and hangs vertically from the marker. The instrument comprises a sighting telescope with an eyepiece and an object lens. This is mounted on a horizontal axis and can pivot in the vertical plane. There is no angle measurement disc associated with this rotation, which is simply used to adjust the sighting with respect to the altitude of the point. The base is a tripod with three blocking screws, which enable the device to be levelled. This parameter can be verified by a cylindrical spirit level located on one of the brackets. Two clasps fix the telescope to the two mounting brackets. A screw on the axis is used to block rotation. At the base of the two brackets there is there is a circular plate which can turn in the horizontal plane and on which the measuring disc is located. The angle values are visible thanks to two lateral eyepieces fixed to the plate. A knob is used for fine rotation adjustment. A screw located on the edge of the plate enables the graduated disc to be blocked and unblocked.