First Degree Fitness Aspen StairMill 4000 Optimized for home gym and light commercial use Compact footpring fits well under ceiling height Electromagnetic braking system. No electrical drive motor reduces power consumption to a mere 60 watts The Step-Lock System employs a photo-optic sensor that will automatically stop the unit if the user dips below the lower limit of travel Computer precisely regulates speed, matching feed rate of steps per minute to the use programmed requirements