It's inexpensive - $10.
It's incredibly useful. I wouldn't have believed how much I'd refer to it, whether simply in my own daily reading or for various other projects.
It's one of the books that "lives" on my Kindle. And I don't have a lot of those, usually preferring a book in the hand to one in the Kindle. (ha! yes, feel free to use that if you want). The formatting is well done and it's easy to navigate.
It's offered in print, Kindle, Nook, and iBookstore formats at the publisher's website. I just pick it up from Amazon myself.