To figure out where to attach the cable to your trees you will use a combination of clearance, slope, sag and your natural elevation change.  Here is the formula: Maintain at least a 7-foot clearance over the ENTIRETY of the zip line avenue while supporting the heaviest riders. Your attachment point at the end is clearance (7 ft) plus sag (2% of total zip line length).Your attachment point at the start will be the end anchor attachment point plus slope (3% of the length), minus any natural elevation change.If you are in any doubt as to how to properly measure clearance, slope or sag, please contact us at 888-476-3701.Instructions for how to measure can be found in the Zip Line Gear handbook included with your purchase. For more information on all three of these topics, you can view the digital version of our handbook, right here.