Below is a spacetime diagram which depicts the movement of a rod, four units long, relative to another rod of equal length. The red lines are the "moving" rod; the purple lines are the "stationary" rod. The gray lines are the world lines of the unit marks (0, 1, 2, 3, 4) on each rod. As I attempt to interpret the diagram, I am moved to ask a question which has been asked before on this forum, including by me. There is nothing new in the question itself--only my level of understanding has (hopefully) progressed. To set up the question, I stipulate that the stationary rod and the moving rod are identical, having been fabricated on the same high-precision equipment. The stationary rod was then fastened to a bench in the lab, and the moving rod was set in motion. As the moving rod passes over the resting rod, it is moving at a constant velocity of 0.6c. As can be seen in the diagram, instruments mounted on the moving rod will measure the resting rod to be 3.2 units long. Likewise, instruments mounted on the resting rod will measure the moving rod to be 3.2 units long. My question focuses on the stationary rod, because it has been minding its own business on the lab bench, and its dimensions are known to be the same as when it was fabricated. Knowing that the stationary rod is four units long, would we not have to conclude that the instruments on the moving rod are incorrect when they report its length to be 3.2 units?