I think that most people would say that you could easily drown in a fathom of water but how many of you know how deep a fathom actually is. I would have said that it was at least 10 metres. In a totally unscientific survey one other person suggested a depth of about 30 metres. A fathom is actually the width of a man's outstretched arms. Also the depth of water in which it's too deep for most of us to stand on the bottom without drowning. That definition comes from a brilliant little book I got for Christmas called About the Size Of It: The Common Sense Approach to Measuring Things by Warwick Cairns.
About The Size Of It is a short book, the spine is about a barleycorn wide, but it packs in a full, from the ground up, definition of all our main units of measurements. Not the boring SI units (although they do make a brief appearance so that they can be rightfully mocked) but rather those measures that we use in everyday life and have survived for generations as they make the most sense in everyday tasks -- like buying fruit!
My Rating: The writing style is informative and highly enjoyable. I could easily see a slightly expanded version as the Royal Societies Christmas Lectures it is that informative and entertaining.