Those planning to travel, for business or pleasure will do well to learn the system of length conversion known as the metric system. In fact, a knowledge of metric length conversion will serve you well wherever you go on the planet, since only three countries in the world - Liberia, Myanmar and the U.S. - have refused to accept the metric system. (In the U.S., rejection of the metric system cost NASA $125 million dollars when a valuable Mars probe was lost back in 1999, because the scientists were working with two different measurement systems.)