People read as much as 10% slower from a screen than from paper.

A recent study found that readers read 6.2% slower on an iBook than from a printed book. That difference jumps up to 10.7% when using a Kindle. However, the people from that same study rated their experience reading books on an iPad more highly than their experience reading on the Kindle, and they both were rated higher than the experience of reading print. And of course, iBook, Kindle, and print were all rated as much more enjoyable than reading of a standard computer screen, which most likely takes much longer than all three to read.
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