Small mistakes. Large consequences

 During the Persian Gulf war in 1991 American Patriot missile failed to intercept an incoming Iraqi Scud missile killing 28. The cause of tragic mishap was an in accurate conversion of time, measured in tenths of seconds, to the binary values as they are stored in the computer. Specifically elapsed time was measured by the systems internal clock in tenths of a second and stored in binary numbers. Then the results need to be multiplied bu 10 to produce the time in seconds. This calculation was performed using 24 bits. Hence the value 1/10, which has non terminating binary expansion, was truncated after 24 bits, resulting in a minute error. This truncation error, when multiplied by the large number giving the time in tenths of a secon, led fatal mistake.

In April 5, 1992 the Green Party in Germany’s state of Schleswig-Holstein was elated. By a hair’s breadth, the party had mastered the 5% threshold required for entry into the state parliment. The rude awakening came shortly after mid night. The true election results were published, and the Greens discovered to their dismay that they had actually only received 4.97%. The program that calculated the election results throughout the day had only listed one place after the decimal, and the count had been rounded to 5.0%.

In 1982 the stocl market in Vancouver introduced a new index and set the initial value at 1000 points. After less than two years the index was down by nearly half, even though the average value of stocks had increased by some 10%. The discrepancy was, again, due to rounding of errors. While calculating the index, the weighted averages of the stock prices were truncated after too few decimal places.

Some tail end humor http://www.xkdc.com

Blag

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4 Responses to “Small mistakes. Large consequences”


  1. 1 yeskarthi December 14, 2006 at 3:58 pm

    There is an interesting thing on problem faced by Mars pathfinder. It was due to fact the some thing called priority inheritance not being handled properly. But the beauty is the JPL was able to patch the code from earth to mars.

    Really cool stuff…

  2. 3 earth2050 December 14, 2006 at 12:20 pm

    by the way this is me again, my logins are killing me….im considering switching to wordpress!

  3. 4 earth2050 December 14, 2006 at 12:18 pm

    yes…even when the beagle landed on mars, it was lost because of unit conflicts!!!!

    Nice cartoon!


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