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The 17" measurement is diagonally. So the given dimensions make sense. Using the Pythagorean Theorem, we get:

sqrt(15.4^2 + 10.2^2) = 18.47

and 18.47 is greater than 17. So it's completely consistent.

If you look at the 15" and 12" index pages, too, you'll see that the 15" PBG4 width is 13.7", and the 12" PBG4 width is actually only 10.9".
 
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