Q. When an e-reader is loaded with thousands of books, does it gain any weight?

A. “In principle, the answer is yes,” said John D. Kubiatowicz, a professor of computer science at the University of California, Berkeley.

“However,” he said, “the amount is very small, on the order of an atogram,” or 10^–18 grams. “This amount is effectively unmeasurable,” he went on, since even the most sensitive scales have a resolution of only 10^–9 grams. Further, it is only about one hundred-millionth as much as the estimated fluctuation from charging and discharging the device’s battery. A Kindle, for example, uses flash memory, composed of special transistors, one per stored bit, which use trapped electrons to distinguish between a digital 1 and a 0.