The first row of controller positions at the lowest level in the Mission Operations Control Room was dubbed "The Trench" by controller John Llewellyn. It consisted of four positions. The position to the far left was called BOOSTER. This flight controller dealt with systems attendant to propulsion during powered flight. Following Trans Lunar Injection, when the spacecraft was boosted out of earth orbit toward a rendezvous with the moon, the position was vacated for the balance of the flight. Next came RETRO. The Retro Fire Officer was responsible for calculating abort maneuvers and working on the solutions necessary for spacecraft re-entry into the earth's atmosphere. (John Llewellyn was a RETRO officer.) Next came the position called FIDO, which stood for Flight Dynamics Officer. FIDO was responsible for the flight path and the calculation of trajectories of the spacecraft. The position closest to the camera was called GUIDO, for Guidance Officer. GUIDO was responsible for the navigation systems of the spacecraft and for determining spacecraft position relative to the flight path between the earth and the moon. Controller Steve Bales was GUIDO during the Apollo 11 lunar landing and made the cool-headed call to continue the landing in the face of an unexpected overflow alarm from the Lunar Module's on-board computer.