The Fiber OWL 7 BIDI fiber certifier is a matched set of two optical loss test sets, or OLTS, called master and remote.
OLTSs are unique test devices that include both a power meter (receiver) and a light source (transmitter) in the same unit.
This dual functionality of OLTSs is what enables the Fiber OWL 7 BIDI certifier to test two fibers a time.