Eight Engineering Disasters Caused by Unit Conversion Errors Cost Billions and Dozens of Lives

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A review of eight major engineering failures highlights how unit conversion mismatches in software interfaces — not mathematical errors — have repeatedly caused catastrophic outcomes. The most well-known case is the 1999 loss of NASA's Mars Climate Orbiter, a $327 million spacecraft destroyed when one team used metric units while another used imperial. Another incident involved a Patriot missile defense system failure during the Gulf War, where a binary floating-point error in tracking time caused a miscalculation that resulted in 28 soldiers' deaths. Across all eight cases, the root cause was the same: two correct numbers assigned different units on either side of a software boundary. The combined financial toll of these incidents exceeds $65 billion, with human losses that cannot be measured in monetary terms.

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