I normally use a computer and a bottom timer for technical dives.
My buddy and I both use Suunto computers and we've had problems in the past during a significant dive where my computer and my buddy's computer showed very different depths. The bottom timer is there to give us an idea, if it every happens again, of which computer has spazed out.
All our technical dives are done with fully redundant air supply. All regulators are Aqualungs.
R..
