a multi-pitch climbing attempt due to being only slightly longer than a standard rope length. Rope diameters are generally between 8.3mm and 11.5mm, with the different diameters used for slightly different purposes. Sport and multi-pitch trad climbers often value thinner ropes because they are lighter, and have less rope drag. Thinner ropes also run more smoothly through belay devices, especially assisted braking devices or 'tube-style' devices operated in 'guide mode', which can be tedious to pull thicker or stiffer rope through. Lighter, thinner ropes, however, have less strength than a thicker rope and will sustain fewer hard falls. Note that some belay devices are better suited for different rope diameters. This is particularly relevant with assisted braking devices, such as the Petzl Grigri (which, for example, works best with a 9.4-10.3 mm thick line) or the Faders SUM. Users must make sure to read the instructions for the device carefully to ensure safety and recognize any limitations to rope diameter. Standards and testing All modern rock climbing dynamic ropes rated by the UIAA must meet certain standards and pass testing for Construction, Sheath Slippage, Static Elongation, Impact Force on first fall, and Number of falls held. The force rating indicates the maximum amount of force the rope can deliver to a falling climber, measured in kilonewtons (kN), under test conditions designed to simulate a hard fall; typical climbing ropes range from 9kN up to an Arborist's 24kN. The force rating is often misunderstood by climbers, because all other climbing gear is rated by the breaking strength (in kN) of the material. Whereas a higher rating (indicating greater strength) is desired for other gear, for dynamic ropes a lower rating is generally desired, as this indicates it would give a 'soft catch' that is less likely to injure the climber or break or dislodge protection or anchors. Unlike most climbing equipment, dynamic ropes do not have a rated tensile breaking strength. Instead, the strength of a rope is tested by the number of standard test falls a rope can sustain before breaking. The test falls use an 80 kg weight for single ropes (55 kg for half ropes), and a fall factor of 1.7 (4 meter fall on 2.3 meters of rope). This tests simulates a very hard fall that would rarely occur. When climbing, it is possible to produce a fall factor as high as 2, however, real-world climbing situations