USAGE:

api.php?ref_system=<casaubon/kaibel>&reference=<Casaubon/Kaibel Reference>


e.g.: 

http://www.digitalathenaeus.org/tools/Casaubon-Kaibel_converter/api.php?ref_system=casaubon&reference=3.373a
http://www.digitalathenaeus.org/tools/Casaubon-Kaibel_converter/api.php?ref_system=kaibel&reference=1.10