Sundials and improvised compasses

I joined iPhone Nation a month or so ago. The iPod touch was my gateway drug. It seemed harmless enough at the time, but things got out of control. Now I’m one of those people. One of those iPhone people. You know the kind. Even I think we’re insufferable.

Anyway, I’ve been having fun with the applications available at the App Store, and one that caught my eye was Masayuki Akamatsu’s Compass. Here’s a little video on how it works.

In a nutshell, here’s the theory. If you know where you are, and you know which way is north, and you know what day of the year it is, you can build a sundial that keeps very accurate time. (If you don’t know what day of the year it is, you can build a sundial that’s reasonably accurate, but that’s another matter.) Stated another way, if you know what day it is, and you know where you are, and you know what time it is, then you can build a sundial that will tell you which way north is. It turns out an iPhone has all the information it needs to build just such a north-pointing sundial. Which is to say: a compass. No magnet required.

I had a similar thought four years ago when I was noodling around with some sundial code in MATLAB. I even wrote a contribution for the MATLAB Central File Exchange called Building Sundials. That contribution came with some explanatory text that closed with this statement.

Suppose you were lost in the woods, equipped with only a computer, a printer, and a copy of MATLAB. How would you orient yourself?

I meant it as a joke, but that’s essentially where the iPhone has gotten us.

Okay, I admit that a real compass is cheaper than an iPhone. And it works at night. Without batteries. And when it’s cloudy. But still… Hey, did I show you my beautiful new iPhone?

Negative signage and the letter of the law

When I first moved to Massachusetts from California, I learned about the value of the private snowplow contract. When it snows hard, it’s really nice to have a pro come plow your driveway, even if it does set you back a little cash. But one winter when there wasn’t much snow, our (presumably cash-poor) plow guy would pay us a visit and send us a bill at the drop of a flake or two. We had to reach an agreement that he was not to plow unless more than four inches had already fallen. My housemates didn’t go for my solution: a sign in the yard that was exactly four inches tall that read

Do not plow the driveway

I was reminded of this recently because of a funny post at (“putting the rarin back in librarian since 1999”) about how the Patriot Act lets the FBI invisibly explore your library usage. If you’re a librarian, you are specifically forbidden from telling anyone that the goons have been sniffing around. But let’s say you’re a librarian and this policy really bugs you. What to do? What to do?

Here are’s five technically legal signs for your library. My favorite?

[First spotted on LibraryThing. Follow the link and read about the scofflaw library patron who ended up with a criminal record.]