The leg stretcher

I tried to figure out how the leg stretcher worked but was stumped. My 16 year old daughter took a look and knew how it worked in 2 minutes. I can now stretch to 110 or 120 degrees. Can't lean forward much, but perhaps that will come with practice. I still am working on flexibility on the butterfly stretch. If I'm conscientious, that will improve also. I circuit train tonight with my sister and a friend. I like the weight training and some of the aerobic, do not care for jumping jacks and jump roping. Seems hard on my knees. After circuit training, I have sparring drills and HKD.