If we’re to ban such questions, it would be good to formulate an actual criterion, other than the Potter Stewart test, that distinguishes them from allowed questions.
For example, I don’t think would be fair to ban questions about certain devices merely because they are based on mechanical principles rather than electronic logic: this would cover history questions about the Analytical Engine, or electromechanical machines like the Enigma and IBM’s early punch card systems, which I believe should be accepted.
So I would like to propose two rule-of-thumb criteria:
- If the question would make just as much sense if the device were made of Magic Space Mice, the question is probably not about computing;
- If it’s just a ‘small’ finite-state machine, so the only ‘algorithms’ it’s capable of running are O(1), it’s probably not a computing device.
If a question fails both criteria, I think it should be considered off-topic. I’m not sure if those are sharp enough to capture what ‘computing’ means, so feel free to poke holes in them. The former is meant to capture the principle that questions should focus on ‘the computing aspects’, while the latter is meant to capture the intuition that the device is ‘morally’ Turing-complete (even if technically all computers ever built are finite-state machines anyway).
Given these two tests, I think the pinball question fails both, while the coin-on-a-string question fails the complexity test, though not the Magic Space Mice test. Then again, the latter question need not necessarily quality as ‘retro’; vending machines that accept coins are still in use, so mechanical coin receivers can be considered ‘current’ technology.