I've been using the Workout app to record my time on the elliptical and for lifting weights. For the latter, I use the "Other" setting. However, for the past week or so I found the heart rate monitor had difficulty locking on when I lifted weights, thus affecting the accuracy of the Workout app. It was very accurate when set to "Elliptical". Yesterday, I moved my watch a bit further up my arm, just after the wrist bone. Usually it sits in between my wrist bone and my hand. By doing this, I was able to get a near-constant heart rate reading. Might be worth a try if you've been having similar problems.