An Improvement to Floating Point Numbers

On February 25, 1991, during the eve of the of an Iraqi invasion of Saudi Arabia, a Scud missile fired from Iraqi positions hit a US Army barracks in Dhahran, Saudi Arabia. A defense was available – Patriot missiles had intercepted Iraqi Scuds earlier in the year, but not on this day.

The computer controlling the Patriot missile in Dhahran had been operating for over 100 hours when it was launched. The internal clock of this computer was multiplied by 1/10th, and then shoved into a 24-bit register. The binary representation of 1/10th is non-terminating, and after chopping this down to 24 bits, a small error was introduced. This error increased slightly every second, and after 100 hours, the system clock of the Patriot missile system was 0.34 seconds off.

A Scud missile travels at about 1,600 meters per second. In one third of a second, it travels half a kilometer, and well outside the “range gate” that the Patriot tracked. On February 25, 1991, a Patriot missile would fail to intercept a Scud launched at a US Army barracks, killing 28 and wounding 100 others. It was the first time a floating point error had killed a person, and it certainly won’t be the last.

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Book Review: The Good Life Lab


Stop whatever you’re doing and get this book. I’ve just finished reading it and I have to say that [Wendy] and [Mikey] could easily be the poster children for modern day hacking, and this book could be the manual for a life built on hacking.

When I visited [Wendy] and [Mikey] last year I was blown away.  Their little homestead was a veritable smorgasbord of hacks. Everywhere I looked, things were cobbled together, modified, repaired, and improved. There wasn’t a single piece of their lives that wasn’t somehow improved by their efforts to play an active role in their own living.

That sounds a bit cheesy I know. We all play an active role in our lives right? Sure. But what they have done is created a hacker’s homestead. My projects tend to live on my workbench, occasionally poking into my daily life, but they went were there was virtually nothing and hacked together everything they found they needed.  Their life is their workbench.

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Review: The Manga Guide to Electricity


“The Manga Guide to Electricity”, part of “The Manga Guide” series by No Starch Press, is a novel approach to the old problem of getting over the initial mental block when trying to learn electronics.

We decided to compare this book to another introductory text: “Getting Started in Electronics” by [Forrest M. Mims].  [Mims]’ book is a handwritten masterpiece of electronic literature. The writing style is friendly and concise, the examples are simple, and the drawings are excellent. It also makes sure to keep the learning process as application based as possible. Unlike other books, it doesn’t bog the reader down with math and theory that is only useful to advanced students. Since its original printing in 1983, [Mims]’ has become the de facto standard for beginner electronic literature. Continue reading “Review: The Manga Guide to Electricity”