Pythagoras's Theorem made easy
This animation shows Pythagoras's theorem in a visual way.
Guide to using SI Units
The National Institute of Standards and Technology (NIST) has updated its document detailing the definitions and use of SI units.
available online here
A good description of dB is available online from the University of NSW. http://www.animations.physics.unsw.edu.au/jw/dB.htm