Panel L was used by both the Custom Engineer (CE) and the 360/195 operator (usually at the request of a CE when some malfunction occurred).
See Operator Intervention for details.
The left-hand section was predominantly used by the Customer Engineers. The System Console Test section allowed engineers to step slowly through a sequence of instructions
checking the light configurations as they went along. Both a single step mode and a slow execution mode were possible.
The middle row of switches allowed various diagnostics to be performed with the use of the central Cyclic Program Counter.