Hi Steve,
I'm the part-owner / Manager of a busy dive center in Bali, Indonesia. We don't use any barcode system yet but have been thinking of barcoding all our rental gear AND tanks. This is because we have one central location but run trips to several destinations each day.
I've no experience with anything like this so am interested to learn as much as I can about it, both about which kind of barcodes would be used (this is the question you posed) and also the software interface for it. To keep things simple (KISS) I'm imagining that each item of rental gear or each tank would be logged out to whichever of our field staff (DM, Instructor, driver) was in charge of that program.
I wonder which kind of barcode and software interface I could use to implement this?