Brass Surveying Sight When intact, a surveying index would have a brass surveying sight like this one. A second sight would also be part of the index, with opposing slots between the two sights. A brass sight for a surveying device was found 3 ft. from the pivotal mount, and the two pieces may have came from the same instrument. The sight (height 6 in.) is slotted twice for rough and pinpoint aiming, and the larger slot (1.8 x 0.4in.) is bracketed by two holes that would have held a crosshair. A set-screw attaches the sight to an index that is broken at a threaded fastener hole.