Metric Math: Learning to convert between traditional and metric units in your head (Mental Math)

In 1999, NASA lost a $125 million orbiter because of one simple and seemingly innocuous mistake — the engineering team that built the orbiter used English units of measurements to make their calculations, while the agency responsible for launching the rocket used the metric system.
Mistakes like this happen all the time. Since there are two sets of systems that are both widely used, conversion from one system to another has become incredibly important. Whether you are engineering a rocket, calculating the speed of your car, or baking a cake — knowing how to convert from the traditional system to the metric system in your head gives you a huge advantage.
This book teaches children and adults to convert units of length, area, volume, weight, temperature, and speed in their heads. Growing up with only one system makes it hard to move between the traditional system and the metric system, especially if the conversion has to be exact. The two systems grew up separately, and they were not meant to match. An exact conversion is even harder in the head. Much of the world uses the metric system, so these conversions come up often.
To make them quick, we use numbers that are close rather than exact. Some are rounded up and some down. Each lesson shows how a close approximation can still give a useful measure. Where it helps, we also give the more accurate conversion.
The arithmetic is fairly simple. A student does need the four operations, some work with decimals and fractions, and a basic feel for negative numbers, which come up in temperature. The book also teaches a few mental shortcuts.