The Derrickhand or Derrickman position varies greatly from one drilling rig to another. He almost always reports directly to the driller. The name derrickman comes from the position that he normally occupies, which is at the top of the derrick. From this position he guides the stands of drill pipe, typically 90 ft (27 meters) long, into the fingers at the top of the derrick while tripping (removing the drill string) out of the hole. When tripping into the hole (aka Running In) he will pull the pipe out of the fingers and guide it into the elevators suspended from the top drive. Traditionally the derrickman also works closely with the mud engineer (see drilling fluid) when not tripping pipe since he is not needed in the derrick. In this capacity it is his responsibility for monitoring the viscosity and the mud weight (density), adding sacks of chemicals (25-100 lb each) to the mud to maintain properties, and monitor the mud level in the mud pits to aid in the well control. He may also be responsible for the shale shakers and the mud pumps. The derrickman is also responsible for the transfer of chemicals (eg: Barite or Bentonite or oil-based fluids) from bulk silos or tanks to the mud system.