GYMstar Calculator is a game changer for the athlete. What sets GYMstar Calculators in a different class of calculator is last results compared to today’s results while working out. Then the GYMstar Total. This can be used in so many different ways to evaluate progress. I purchased a DZ09 and it works fine. I realized the potential to break my cell phone. The wrist watch is great. Has many other options but I use it for my weight lifting workouts. I highly recommend getting a smart watch.