This is my first attempt at building a dual display PO2 meter. I have successfully pressure tested the acrylic and delrin casing to 80m, however the housing can be flooded with paraffin oil to make it resist higher pressures. The end of the cable has a 1/4" NPT fitting that screws into the head from my M1 rebreather or a KJ Hammerhead Inspo head. Cost in parts was about AU$80.

The PO2 meter is magnet free (so can be used with a compass) and non-magnetic except for the battery. The top cap rotates a few degrees to trigger the mechanical microswitches to either: on, off, or on with backlight. The backlight can be switched on or off underwater during a dive. If the epoxy sealing the cable fails, the bolts holding in the caps will prevent them from popping off.

The electronics are two simple DPM's wired together and then coated in PCB lacquer. If the main potentiometers are out of calibration range, the backup potentiometers can be used to further adjust the reading. The outer tube of acrylic plastic has been annealed to prevent crazing (small cracks in the plastic that form over time).

Calibration is done through a 7/16" UNF hole that is plugged with a HP port plug when not being calibrated. To adjust the left DPM, the top cap is rotated to clockwise, exposing the center of the potentiometer for the left display. Vica versa for the right display. Also, each display has an orange LED light to illuminate it night.