What Makes Great Technical Writing?

[Yes, this is one of those "reader input" posts]

What comes to mind when you think of great technical writing?

Maybe a how-to manual that stands out?
Maybe a good book that happens to be about some technical subject?

Data points to consider:

- When I put this question to my Gmail audience, one friend wrote, "Good grammar and pictures." And brevity is the soul of wit.

- An Ax to Grind: A Practical Ax Manual is a 68-page booklet from the USDA. The author's love of axes is plainly legible. It's more than you need to know about axes, but that's the point, right? Bonus points for being "your tax dollars at work".

- I've read only one of Gene Logsdon's books (this one), but I liked him immediately. He's been aptly described as a "man of letters"; he's an example of a great writer who just happens to write about technical things.

- Water Storage: Tanks, Cisterns, Aquifers, and Ponds is a great little book about water storage. It's 3/8" thick and it's everything you will ever want to know about storing water. Lots of pictures and clear diagrams.