A very good video showing how the pull on your anchor points differs depending upon the angle at which the ropes are set. With two anchor points, a 100kg mass will exert 50% of it’s force on each anchor when the ropes are 30 degrees apart, at 90 degrees the force increases to 70% on each anchor, at 120 degrees this goes it to 100% (100kg).
One interesting and important thing to note is that if the angle is between 0 and 30 degrees then if the pull is not even on the anchors then the force on one anchor increases exponentially! A picture (video) paints a thousand words:
Rigging Angles (coutesy of High Point Access & Rescue)
