Thanks for the chapter!
Once again modern concepts has revolutionized a stagnant method. If I'm understanding it correctly previous makers and designers were trapped with the concept of drawing a circuit only on the x axis of the surface of whatever they were writing the circuit on. So if describing a paper a circuit is drawn on with the cardinal points, the circuit would be written as either N, S, E, W or some combination of the four, but not up or down. Like the circuit is the route drawn with a pencil on a road map or the route highlighted on the map of an online mapquest or similar program. By 3d he means that not only is the circuit drawn with the four cardinal points but up and down as well allowing more area to draw the circuit in while limiting the size. So let's say a circuit's efficiency and speed is dependent on the distance between the absolute center of the circuit and the farthest line a 3d circuit with a 2inch square design would have at most 2 inches between the two. However, flattening it out on a paper makes it 6 inches diameter then it would be less efficient and slower due to the distance being around 3 inches from the center to the outermost line. Basically, he came up with a way to expand, increase efficiency, and redesign a magic circuit in a revolutionary way that has carptured Leila's interest in a big way and getting her inventive and researcher skills in overdrive.
Btw, took me a few rereads to remember them but the triplets with the picture vocabulary are the three ghosts he used DP to create to haunt the "Demon Lord's Castle" he built and waylay intruders like the hero. In the hero's case they used their powers to move armor, have her go around in circles, and scare the hell out of her.