Typically, an MFL tool consists of two or more bodies. One body is the magnetizer with the magnets and sensors and the other bodies contain the electronics and batteries. The magnetizer body houses the sensors that are located between powerful "rare-earth" magnets. The magnets are mounted between the brushes and tool body to create a magnetic circuit along with the pipe wall. As the tool travels along the pipe, the sensors detect interruptions in the magnetic circuit. Interruptions are typically caused by metal loss and which in most cases is corrosion and the dimensions of the potential metal loss is denoted previously as "feature." Other features may be manufacturing defects and not actual corrosion. The feature indication or "reading" includes its length by width by depth as well as the o'clock position of the anomaly/feature. Mechanical damage such as shovel gouges can also be detected. The metal loss in a magnetic circuit is analogous to a rock in a stream. Magnetism needs metal to flow and in the absence of it, the flow of magnetism will go around, over or under to maintain its relative path from one magnet to another, similar to the flow of water around a rock in a stream. The sensors detect the changes in the magnetic field in the three directions (axial, radial, or circumferential) to characterize the anomaly. The sensors are typically oriented axially which limits data to axial conditions along the length of the pipeline. Other designs of smart pigs can address other directional data readings or have completely different functions than that of a standard MFL tool. Oftentimes an operator will run a series of inspection tools to help verify or confirm MFL readings and vice versa. An MFL tool can take sensor readings based on either the distance the tool travels or on increments of time. The choice depends on many factors such as the length of the run, the speed that the tool intends to travel, and the number of stops or outages that the tool may experience.