Features optical adjustment. Heavy-duty impact and corrosion resistant aluminum housings are flat and compact with no protruding or adjustable parts. Needle cards are immersed in a clear, low-viscosity liquid damping for smooth, vibration-free movement. Needle cards pivot on polished sapphire bearing. Azimuth models graduated to 1/2°; estimate to 1/4°. Quadrant models are graduated in 1° units. Cotangent table printed on back. Balanced for global use. Black nylon case included. Dimensions: 3” x 2” x 9/16”.