Here's a story that actually happened, one that shows how important it is to accurately use consistent Units when Measuring:

  "When we are making measurements, the units we use are just as important as the numbers we get. Please note that failure to indicate the units involved in measurements can lead to serious problems. For example, the "Mars Climate Orbiter", a NASA (National Aeronautics, and Space Administration) spacecraft built for the exploration of Mars, vanished during an attempt to put the craft into orbit around the planet. In an investigation that followed, NASA determined that a units mix-up had caused the disaster. One team of engineers had used metric units in its designs, while another team had used English units. The teams did not indicate the units they were using, as a result, the designs were incompatible."