The "Erlang" is a dimensionless unit that is used in telephony as a measure of offered load or carried load on service-providing elements such as telephone circuits or telephone switching equipment.
http://en.wikipedia.org/wiki/Erlang_(unit)
https://cdd.iec.ch/cdd/iec62720/iec62720.nsf/Units/0112-2---62720%23UAB340
http://dbpedia.org/resource/Erlang_(unit)
http://www.iso.org/iso/catalogue_detail?csnumber=31898