Think of something shaped like a wishbone. Arms run up at an angle. Chains come down from the upper ends, one set for the head, another for the body.
I've found that salvaged auto seat belts is better than chain. Takes more hits to cut it. Having the head/body option might be useful for an unknown distance competition.
Had no trouble buying a set of legitimate discs. Forty odd dollars plus postage.
The system described using the PDA, quality laser range finder and Horus reticle looks to work very well for what they were doing. Don't know if it would be particularly useful for the shooting I do. There is a lot of good information for anyone interested in long range shooting. If you don't want $700 worth of PDA, and an expensive Horus scope, you can achieve the same results with the $100 disc calculator system and your mildot reticle. Just a bit slower.
Of course, there are other shooters here who know at least as much as the folks who made the videos. If they study the videos, they will automatically add anything new to what they already know, and be way ahead of the producers.