TED Talks
Ted: Ted Ed: Why the Metric System Matters
For the majority of recorded human history, units like the weight of a grain or the length of a hand weren't exact and varied from place to place. Now, consistent measurements are such an integral part of our daily lives that it's hard...
National Institute of Standards and Technology (NIST)
Nist: Rules & Style Conventions for International System of Units (Si)
The official rules for using the SI (metric) system in the US, based on the National Institute of Standards. Must download their handbook.
E-learning for Kids
E Learning for Kids: Math: Market Place: Mass
On this interactive site students learn to use various units of mass to solve problems and put objects in order by their mass.