"Things to Make and Do in the Fourth Dimension" is really fun, but it's not really tech, it's more just math. But I do a lot of work with scientific / numerical computing so some may group them together. In addition to math, it covers some interesting algorithms and fun ways to use spreadsheets for images, etc. I also really enjoy books about the tech used in the early space program. "Digital Apollo" is probably the one that makes the best light / easy reading.
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