The terms below are the ones a chart assumes you already know. They mean the same thing on every manufacturer's chart.
Where the load is
| Axis of rotation | The vertical centreline the superstructure swings about. Every radius is measured from it. |
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| Radius | The horizontal distance from the axis of rotation to the centre of the hook, with the load suspended. A loaded boom deflects, so the loaded radius is always longer than the empty one. |
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| Boom angle | The angle of the boom above horizontal. Some charts are organised by angle rather than by radius. |
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| Boom length | The length from the boom foot pin to the boom tip sheave pin, as currently extended. |
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| Working area | The sector the load is over — over the front, over the rear, or anywhere in 360 degrees. A crane is weakest over the side, so the 360-degree column carries the lowest figures. |
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What the crane can lift
| Gross capacity | The rating found by matching the boom length against the radius, or against the boom angle. It is the total the crane may support in that configuration, not the weight of the object. |
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| Deductions | The weights that have to come off gross capacity, because the rating has to cover them and they are not available for the object. What counts is machine specific — the chart's own deduction table lists it. |
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| Net capacity | What is left over once every deduction has come off the gross capacity. The heaviest actual load you may pick in that configuration. |
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| Prohibited configuration | A set-up the chart does not permit. The gross capacity is zero; there is no rating and no lift. |
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The rope
| Parts of line | The number of rope parts supporting the hook block. More parts share the load between them. A ball is always a single part of line, and lifting from the jib is a single part of line — neither is necessarily stated on the chart or obvious from the set-up, so count rather than assume. |
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| Wire rope breaking strength | The load at which that rope would fail. The starting point for the figure below, not a working limit in itself. |
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| Permissible line pull | The safe maximum for one part of line: the rope's breaking strength divided by the design factor. This is the rope figure used for capacity. Multiplied by the parts of line and compared against gross capacity on every lift; if the result is lower than the chart rating, it becomes your gross capacity. |
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| Available line pull | The actual pulling force the winch or hoist motor can deliver. It falls as rope builds up in layers on the drum, because the effective drum diameter grows. This is a mechanical and hydraulic limit on the machine — it tells you whether the winch can pull the load, not what the crane may lift, and it is never used in a gross or net capacity calculation. |
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What is limiting the rating
| Stability limit | The rating is set by the crane's resistance to tipping. On fully extended outriggers a stability-based rating is normally a percentage of the tipping load — 85 percent — and 75 percent on tires or with the outriggers retracted. |
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| Structural limit | The rating is set by the strength of the crane's own parts, not by tipping. Charts usually mark these values. Exceeding one can break something without the crane ever starting to tip. |
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