Crossover at book —
≈ — of reading
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An e-reader's manufacturing energy is spent once, up front; a printed book's production energy is spent again with every new copy. This simulator plays that trade-off out book by book in 3D — two rows of bars grow across the scene, one bar per printed book at a constant height, the other a single tall spike for the device followed by nearly-flat bars for each e-book read, while two rising curves trace the cumulative energy each path has consumed. Adjust the device's embodied energy, the per-book print energy, the per-book digital energy, and a reading pace, and watch the live crossover marker show exactly which book number — and roughly how many years of reading — it takes for the e-reader to pay back its own manufacturing footprint.