Offboard diluent gas is plumbed in through a female QC-6 connector on the bottom of the diluent manual add valve (MAV) and ported directly into the inhalation side of the head where it is directed over the cell face of sensor #1. This allows for instant cell verification with a known gas source. The Shearwater Petrel 2 makes this a simple process by displaying the diluent pO2 and the actual pO2 side by side on screen number two. No need to perform a complete diluent flush to verify your cells; simply add a few short bursts of diluent via the MAV and you have instant verification. The diluent MAV also has a bypass port, which can be used to plumb gas to a Shrimp BOV or a backup regulator on a necklace.