Licenced under the Creative Commons Attribution-ShareAlike 3.0 Unported (CC BY-SA 3.0) licence: http://creativecommons.org/licenses/by-sa/3.0/
AVR-based real-time speed-of-light display
The speed of light (v) is calculated from the speed of light in vacuume (c) and the refractive index (n) of air1 based on the current measures of temperature, relative humidity and atmospheric pressure2.
Factors such as the wave length (λ) of the standard red helium-neon laser in vacuum and the concentration of CO2 in the air has not been taken into account (this calculation is valid for λ≈633nm
and the approximate concentration of CO2 of [300..600]μ/mol/mol), although this would yield a more precise calculation of the speed of light.
The included factors are taken from Yahoo!'s weather API3.
1 http://www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node4.html
2 http://emtoolbox.nist.gov/Wavelength/Documentation.asp
3 https://developer.yahoo.com/weather/