in surveying, is an instrument consisting of a braided circle, divided into four equal parts by two lines crossing each other in the centre. At each extremity of these lines is fixed a perpendicular sight, with small holes below each slit, for the better discovering of distant objects. The cross is mounted on a staff or stand, to fix it in the ground, and is very useful for measuring small pieces of land, and taking offsets, &c.

Cross-staff, or Fore-staff, is a mathematical instrument of box or pear-tree, consisting of a square staff of about three feet long, having each of its faces divided like a line of tangents, and having four cross pieces of unequal lengths to fit on the staff, the halves of these being as the radii to the tangent lines on the faces of the staff.—The instrument was used in taking the altitudes of the celestial bodies at sea.