This Bow Compass includes a 170mm extension arm / bar for allowing you to plot large radii as well as small ones. This is ideal for drafting and design work. A quick release mechanism allows for speedy adustment. When the quick release is locked, the micromatic adjustment makes getting the right size cirlce a lot easier. It also comes with a pen adapter so that you can produce circles using your technical pen / fineliner and it comes with extra leads. This compass is double knee jointed and comes in a tidy plastic case. It is a high quality compass that is made from solid brass that is nickel plated - this will produce more accurate and precise circles as the weight of this compass means it doesn't slip so easily on the paper surface.