Some handy links for those who like the Math part of physics and acoustics
> Science, Math, Constants, Equations, Conversions
Sponsored by the UK Institute of Physics - An extremely handy and good link to find lots of things in a systematic way.
> The NIST Reference on Constants, Units
Official standards list from the National Institute of Standards and Technologie. Founded in 1901, NIST is a non-regulatory federal agency within the U.S. Commerce Department's Technology Administration.
PTB as the guardian of the units
The SI system, some history and the basis fot the units.