To 'honor' the 25th edition of the MARK book, I've done a couple of things:
1\ cleaned up a bunch of minor things, and added a fair few new bits of explanatory material to some chapters.
2\ managed to format things for 'archival' hard-cover versions, for those so inclined. Put 'em on your shelf. Impress your colleagues (or some such...).
Volume I https://www.lulu.com/shop/evan-cooch-and-gary-white/mark-book-a-gentle-introduction-volume-i-hardcover/hardcover/product-p6yv9e9.html
Volume II https://www.lulu.com/shop/evan-cooch/mark-book-a-gentle-introduction-volume-ii-hardcover/hardcover/product-e7ry788.html
These hard-cover editions are a bit more expensive ($45 + $54 US, respectively + shipping) than the softcover versions, but are printed on 'much nicer paper' (improving the contrast and legibility of some of the figures). And, for 'big, heavy 8.5 x 11 printed books of 567 and 713 pages each, respectively, not really that expensive (and, as always, production costs only. No one makes any money on 'the book').