An open quadrant 4.25" (10.8cm) radius, mounted on a base 7" (17.8cm) long, with its apex at top and with one side vertical. A moveable pointer 3.75" (9.5cm) long is attached at the apex by a milled brass knob, a plumb line and bob is suspended from the knob. Graduations: the arc of the quadrant is graduated on the inner and one outer edge 0-90, 90-0 degs.
A level is used to determine a horizontal line. Determining a series of level lines at differing heights allows comparitive altitudes to be calculated.