Slowly but surely, the Kerr Stuart “Joffre” at Apedale is coming back together. You may recall that the loco was taken out of traffic due to minor worries about a crack in the cylinder, which turned into serious concerns about several cracks, and which turned into a new cylinder being needed. The owners are pretty confident the loco will be back in business before long – the new cylinder is being cast this week, and will then go for machining. Which is where the uncertainty comes in. The old cylinder was noted to have a slightly puzzling taper of 1/8″ front to back – in other words, it looked as though is could be sitting incorrectly aligned to the loco. However, the loco ran quite happily with said cylinder, and the large end bearing was not wrecked or anything nasty like that. So, the question was – should the new cylinder have the same taper machined on it? This caused some thought and contemplation. Eventually, the CME stopped talking about Meerkats, and came up with an answer. The old cylinder was refitted to the loco – a useful practice for fitting the new one in due course – and fitted with two carefully aligned dummy covers. Each cover had a tiny hole in it, drilled such that it is exactly in the cylinder centreline. A pointer was then equally carefully set-up some way in front of the loco, with a bright light behind it. If one could look through both holes, and see the pointer in the centre of the dot, then clearly the cylinder was aligned correctly. It was, so the new cylinder will have the taper applied. What the CME failed to take into account was the wave-particle duality – was the light acting as a wave or as a particle when it shone through the cylinder? Only time will tell if the failure to grasp basic principles of quantum mechanics will be important when this steam loco is re-assembled. And I’ll bet that’s a sentence never written before. In the meantime, please feel free to get in touch here and tell us all about your pet cat, called (one suspects) Schrödinger.