http://en.wikipedia.org/wiki/Elementary_charge
http://physics.nist.gov/cuu/Constants/bibliography.html
http://dbpedia.org/resource/Elementary_charge
The "Elementary Charge" is the electric charge carried by a single proton, or equivalently, the negation (opposite) of the electric charge carried by a single electron.
http://www.iso.org/iso/catalogue_detail?csnumber=31894