US Patent 7651289 Writing instrument

An adjustable pencil for varying the pressure on a piece of lead includes a cylindrical barrel, and a guide tube containing a piece of lead disposed in the barrel. A coil spring, a rectangular channel with a plurality of stops and a follower compresses the spring for increasing or decreasing the longitudinal force applied to the lead as it engages a writing surface. A knob rotates the guide tube to open or close a pair of jaw like grips for maintaining a pre-selected length of lead extending from the tip of the pencil.