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Using the moiré effect to show different arrows to each observer (2018)
A brilliant optical trick makes this sign read correctly from any possible angle.
Imagine you're in charge of guiding ships into a harbor and you want to use a sign to direct them all to one specific point, perhaps a dock or a channel. Here in 2018, your mind might go to location tracking or some other high tech solution, but in 1982, some clever engineers had already figured out an answer with no electronics required. The Inogon Leading Mark makes use of what's called the moiré effect, that strange type of distortion you see when looking at a series of overlapping, not-quite-parallel lines.
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