Sand coming in through holes in the casing or a malfunctioning production packer can also cause tubing to become stuck in production wells. The term free point is used to describe the delineating point between the stuck pipe and the free pipe in a pipe string. Every joint of pipe above the free point is free, meaning it can rotate freely and be moved in and out of the hole, provided it was not attached to the remaining joints of stuck pipe below the free point. A good way to visualize this is to hold a piece of string with your left hand. With your right hand grab the bottom third of that string. The 2/3rds of the string above your right hand would be considered free, since you can move the string however you may like. The section of string inside and below your right hand is stuck, since no matter what you do to the free string it will not affect the string in or below your right hand. The pipe stretch free point estimate is a good starting point for identifying the free point. The following tools are operated using a wireline truck. The traditional freepoint tool is an electromechanical tool designed to measure the amount of torque or stretch of a given length of tubing, drill pipe, or casing. The traditional freepoint tool uses either bow springs or magnets to anchor itself inside the pipe. After obtaining an estimate of the free point by using the pipe stretch estimate technique, the traditional freepoint tool is run in the hole to 1000 feet above the estimated stuck point. The tool is anchored in place. Stretch and or torque is then applied to the pipe. This allows the pipe recovery engineer to obtain a baseline reading of the free pipe. This will give him a starting point to compare his later freepoint readings to. The tool is then run roughly 500 feet past the estimated stuck point. Stretch and torque are applied, and readings are taken. If the tool indicates that the pipe is stuck at that point the tool is pulled uphole and readings are taken again. By applying the bracketing technique, the pipe recovery engineer is quickly able to identify the exact point that the pipe is free. The Halliburton Freepoint Tool is based around the magnetorestrictive property of steel. This principle states that when torque or stretch is applied to free pipe, the magnetization will change. Stuck pipe will have no change in magnetization. There is a magnet on the bottom of the tool that creates a small magnetic field. There are four co-planar orthogonal multi-axis high sensitivity magnetometers located above the magnet.