Brass course correcting compass in wooden case. Locking device. Heeling indicator fitted on side of case.
To operate: set the latitude of the place on the arc below the hour circle. Orientate the hour circle and the sighting vanes (trained on the sun) until the pointer beneath the smaller vane shows the correct apparent time. Turn the base plate till it coincides with the ships head. The diference between the large pointer (true north) and the North point on the base plate is the compass error. These dials were used well into the 20th Century in connection with adjustments of ships compasses.