Bibliography histogram

I recently noticed something in a book I've had for five years: the bibliography section ends with a histogram of publication dates for references. I've used the book over the last few years, but maybe I haven't needed to look at the bibliography before.

This is taken from Bernstein's Matrix Mathematics. I wrote a review of it here.

An up-to-date bibliography isn't always necessary. One of the references I use the most is nearly 60 years old, and another book I pull down occasionally is 100 years old. But sometimes you do need a current reference, and a histogram of publication dates is a good way for the author to demonstrate that the references are up to date.

By the way, notice the phantom diagonal lines across the histogram? That's a moire.[1]

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[1] Pun on this and this.

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