The sling in a crane is the rigging that connects the crane's hook to its load. This rigging may be a metal chain, a mesh or a rope made from synthetic fibres. Engineers need to calculate the angle that the sling makes with the vertical because this angle determines the sling's stress. At a constant load, a larger angle forces additional stress on the sling. Calculate the sling angle from the measurements related to the sling using trigonometry.

Measure the length of the sling. For example, imagine a sling that measures 3 feet in length.

Measure the vertical distance that the sling covers. This is the distance between the crane's hook and the load. For example, imagine that this distance is 2 feet.

Divide the vertical distance by the sling's length: 2 ÷ 3 = 0.67.

Find the inverse cosine of this ratio using a scientific calculator: cos-1 (0.67) = 47.9 degrees. This is the angle between the sling and the vertical.