Get one of those digital display stopwatches that stick on with vecro to your control column clip. They are more money but sod all in the grand scheme of things. Using the ADF stopwatch is all very well but leaning over to stop and start it and keeping your eye on it during procedures distracts you from your scan.
I was lucky - I bought my stopwatch and CC clip at cut price off a guy who'd just passed his test.... and I still owe him the money but he's 4000 miles away now and I've no contact address!
VFE.