I heard this from Chris Sells, but the test is so good in determining the worth of a book, that I am going to put it on my blog and use it over and over again.
I can sit with a book in my bathtub. Read it with great pleasure. But I cannot sit with a laptop in my bathtub, because I am afraid I'll drop the laptop and electrocute myself, or at the very least cause serious damage. A good book must pass the bathtub test. You should be able to learn a topic, comfortably, without having to pull out the laptop. It must leave no questions unanswered, nothing to be guessed. The logical order of content must be laid out in a manner that is comfortable to read and the reader can follow it very well.
Because, you'd rather not drop your laptop in the bathtub, but reading a book in the bathtub is a rather joyous experience.
This, my dear friends, is the bathtub test for a book.
Now I'll be using this blogpost in my book reviews over and over again.