To prepare for the lesson, students were given as a homework assignment visiting links to NASA press releases (from September 20, 1999, and September 30, 1999) about the loss of the Mars Climate Orbiter. In class, David then used Mars websites to show how critical the measurement system was to the maneuvers required to place the spacecraft in the proper orbit. According to investigators, the orbiter was lost because different teams of scientists used different units of measurement, with the result that the spacecraft was thrown off course and beyond tracking distance. David’s lesson then discussed the International System of Units (SI) for measurement in science and engineering (largely the metric system), and a mathematical technique called dimensional analysis.