"Strength" is the share of the rope's own breaking strength typically left after the knot is tied — every knot weakens rope, because the sharp bend on the inside of the first curve takes the load first. Figures are the usual range quoted in rigging and climbing references for a properly dressed and set knot in good rope; a sloppy knot, shock loading, a knot tied in old, wet or frozen rope, or one tied in slippery modern fibres (Dyneema and Spectra need knot-specific care) can all do far worse.

The diagrams are schematic: they show the geometry and the order the rope passes through itself, not the exact lay of a dressed knot. Learn the shape, then practise with a piece of rope in your hands — a knot is a skill in your fingers, not a picture in your head.

Nothing here qualifies you for life-critical use. Climbing, sailing aloft, rescue, arboriculture and lifting overhead loads each need training with an instructor and equipment rated for the job. Use this for tarps, tents, boats' mooring lines, garden jobs, parcels, craft and general camp craft — and get taught properly for the rest.