These recorders etch marks on a roll of paper, making it possible for a skilled operator to identify a variety of submerged objects. In law enforcement, these objects can include illegal fish nets, stolen vehicles, cracked safes, and murder and drowning victims. The capabilities of a sonar unit depend on several variables: the depth of the water, current and turbidity, temperature and thermoclines, bottom structure, electrical interference, and the size of the object sought. A sonar can operate out of any type of boat, using the following set of equipment: a computerized sonar graph recorder with a swivel mount, 8-degree and 20-degree transducers, a transducer switchbox, a 12-volt marine battery, 4 to 6 floats with enough line and anchor for water depth, and graph paper. The search will be most effective if only the sonar boat is in the crime scene area. The sonar operator should identify the point of entry of the object sought and use a grid pattern in the search. Additional guidelines on using the sonar, examples of its successful use in Illinois, figures, and photographs.