I've been using the PinGuy app on my iPhone with great success... I calibrated the phone on a level surface (checked in several planes with a level), and the app displays the incline and level.
To get the levelers loosened, you can either get a slender wrench in on the foot, or in a worst case scenario, wrap some tape around the threads (inside the leg) and use a vise-grip to get the turning started.