This panel showed some of the internal registers of NIMROD as it performed its computation in slow or manual mode. The state of the registers determined the instruction flow — displayed at the same time in the left-hand panel
At upper centre of the panel is a display of the Main Store, which holds the state of the rows in binary form. Below this are the binary values of the Heap (i.e. Row) and Column counters used to examine the game position. There are also lights adjacent to each row and column (not seen in the sketch) that show the decoded column and row references. Right at the bottom is the legend that is illuminated when the machine has selected a heap to operate on.
The green panels shown in the sketch are simply labels denoting specific subsections of the computer's circuitry, illustrating their links to the machine registers.
A full description of these registers, and the program steps that interact with them, is given in the original booklet, included on this site and in the simulation package.