It's default setting is to be automatic, I'm guessing as an anti-litigation measure. Normally it's fine, but yes, it does take a few more seconds. What it is good for is timing when shocks are due - when you are doing a one or two person resus not having to watch the clock is one less thing you have to do. (Of course, if I could programme an iPhone, that'd be my first application, an automatic timer for resus that jogs your memory as to when to give what drug and then logs what you did at what time.)