Getting the symbols Edit
The needed symbols are given on the viewer which is located at the cannon post. Pressing the red button below the screen displays a blue symbol for a couple of seconds. You need to make notes of all 12 symbols in their correct order.
At some point, one of the symbols is repeated and accompanied by a noisy sound effect. Make the note of that too.
Opening the Tunnel Room Edit
These symbols are needed to get into a room located in the desert, its entrance situated to the left of a red tunnel. You must repeat the sequence seen on the viewer; as the symbols scroll through their cycle, click the button to place the current symbol into the order. When you get to the position of the "noisy" symbol, put whichever of the symbols here that is making that same noise.