In earlier years of Lawrence Livermore National Laboratory’s spaghetti diagrams, such as the above example from 1976, the ends of the swaths were more like the simpler energy flow diagrams. On the above diagram it’s easier to see that the height of the lines on one side would end up around the height of the lines on the other side than it is on some of the newer versions with oversized boxes that serve as labels. But the boxes are a useful tool, and can let us think about embedding another diagram form — box diagrams — into the spaghetti diagram.
Box diagrams are used for teaching electricity, and were developed by Peter Cheng and David Shipstone in the UK. The picture below is from part 1 (Word doc) of their introductory paper (here’s the Word doc part 2). Since power is the voltage across a bulb multiplied by the current [...]

