Rope Logic uses 3-sigma testing, also known as the three-sigma rule, to evaluate and determine the minimum break strength (MBS) of our rope products. Three-sigma is a statistical tool used to calculate probability. Minimum break strength is very different from average break strength (ABS), although, ABS is used in the calculation of MBS.
The three-sigma value is determined by calculating the standard deviation (a complex and tedious calculation on its own) of a series of five breaks. Then multiply that value by three (hence three-sigma) and finally subtract that product from the average of the entire series. It is 99.73% probable any additional breaks will be at or above this final value.
Rope Logic applies three-sigma testing for MBS to our standards because it is much more rigorous and therefore safer than using simply the average break strength.
The three-sigma process:
We know you rely on your Rope Logic products to perform critical functions within life-safety applications like climbing and rigging. Using three-sigma focuses on reducing variability in the manufacturing process, ensuring a high standard of quality and reliability for all of our products.
For those of you who are really into math and 3-sigma, there’s a good explanation in this video about normal distribution: