The Rock Climbers Shock Force Calculator we linked to in August 2009 takes multiple hits each day - presumably from climbers hoping to gain some understanding of the forces generated in the event of a fall.
The Rock Climber's calculator works OK for tree climbing but is not entirely appropriate for calculating the forces generated during a tree rigging operation.
The Rock Climbers calculator assumes the fall is brought to a complete halt and does not calculate the impact force including a controlled 'run' on the line.
Yesterday we linked to an Impact Force from a Falling Object Calculator. This calculator displays the kinetic energy generated just before impact and allows the user to input the distance traveled after impact (that is, the controlled 'run' in the case of tree rigging).
This tool is useful in demonstrating the difference between a sudden stop on the bollard and impact block over a controlled run on the line.
As with all the online calculators, these tools should be used with discretion (and caution), more as a demonstration of theory over practical application. Experience counts!