In 1999, NASA lost a $327 million spacecraft because one engineering team was using metric units and another was using imperial — and nobody noticed until it was too late. We dig into the Mars Climate Orbiter disaster to explore how a single, silent unit mismatch burned up in a Martian atmosphere, and what it says about the terrifying assumptions we bake into the software systems we trust with our lives. Spoiler: it's not really a story about math.