The redundancy is on the basis of the DIR Siystem:
Bouyancy Compensator+Drysuit
Double tanks with manifold....
backup lights...
backup mask..
etc
....
I wonder why there is non mention to depthmeter/botomtimer redundancy, as recommended by various training agencies
thanks from a
Your buddy has a spare computer (between his ears) and depth guage on his wrist - between yours and his no need for further backup