Range diagrams and working-area charts, explained

Core task 4.4 lists both under the Load Charts domain, which is about 27% of the exam. This page explains each in plain terms so the capacity-table lesson in our how to read a crane load chart guide has the right context.

What each one is for

Range diagram. A side-view drawing of the boom. It relates boom length, boom angle, radius and tip height. Use it to see whether a planned lift is geometrically possible: can the boom reach that radius at that height, and at what angle?

Working-area chart. A top-view drawing around the crane. It splits the circle into zones, such as over the rear, over the side or the full 360 degrees, and each zone has its own capacity column. Use it to pick which column of the capacity table applies to where the boom is pointing.

Capacity table. The grid of gross capacities by radius and boom length, which you read after you know your zone and geometry.

Charts vary in layout from one manufacturer to the next, so read the legend and notes on the chart in front of you. That habit matters more than memorizing a shape.

The invented example we will use

Every number here is ours, made up for teaching. It is not from a manufacturer chart or an exam.

An invented crane has a 60 ft boom. Its invented range diagram shows:

Boom angle	Radius	Tip height (approx.)
75 degrees	15 ft	58 ft
60 degrees	30 ft	52 ft
45 degrees	42 ft	42 ft
30 degrees	52 ft	30 ft

Read it as: as the boom comes down, the radius grows and the tip height shrinks. Our invented working-area chart for the same crane says "over rear" capacities are lower than "360 degrees on outriggers" at every radius, so zone selection matters.

How to find radius, angle and limits

1. Pick the zone. Where is the boom pointing relative to the carrier? That chooses the working-area column.
2. Find the radius. Radius is the horizontal distance from the crane's center of rotation to the load line. Without the chart's table, you can work it out as boom length times the cosine of the boom angle, ignoring boom-foot offset and deflection. At 60 ft and 60 degrees, that is 60 × 0.5 = 30 ft, which matches the table above. The crane radius and boom angle calculator checks other angles.
3. Check the boom angle limits. Many charts state a minimum and a maximum boom angle for a configuration. A capacity cell outside those limits is not usable, even if a number is printed nearby.
4. Then go to the capacity table with the zone, radius and boom length you found.

Common confusions

Radius from the wrong starting point. Radius runs from the crane's center of rotation to the load line, not from the boom foot pin and not from the edge of the carrier. Check the chart's definitions.

Boom length versus radius. A 60 ft boom does not mean a 60 ft radius. Radius only equals boom length at a boom angle of 0 degrees.

Using the wrong zone. A bigger capacity in a different column is tempting, but it applies to a different working area.

Structural versus stability limits. The capacity table's bold line, when a chart has one, separates structural limits from stability limits. Our how to read a crane load chart guide covers it, so we will not repeat it here.

Why the order matters on the written exam

Chart questions often hide the first step. A problem may give you a boom length and an angle and expect you to find the radius yourself, or give a working area and expect you to pick the right column. Candidates who go straight to the capacity table miss the step before it. A habit of saying "zone, radius, boom length, then capacity" aloud keeps the order right under time pressure.

Three practice questions of our own

These are original and unscored. Cover the answers and work each by hand.

1. On the invented table above, what is the radius at 45 degrees, and does the tip sit higher or lower than at 60 degrees?
2. A lift is planned at 20 ft radius on this crane. Between which two table entries does it fall, and what do the chart notes in front of you tell you to do?
3. The load sits over the rear, but you read the 360 degree column. What is wrong, and which direction is the error likely to push the capacity?

Answers: (1) 42 ft, and lower (42 ft versus 52 ft). (2) Between the 75 degree and 60 degree rows, at 15 and 30 ft. The chart's own notes decide whether you may work between rows or must use the next longer radius. (3) Wrong working-area column. The error likely overstates capacity, which is the dangerous direction.

Test where you stand

Chart skills are about 27% of the Core, so test them next. The free 10-question check shows exactly which areas to study first, with explained answers and no signup. Pair it with load chart math without a calculator so the subtraction is as fast as the lookup. Then repeat the steps on the load chart practice tool until they are automatic.

FAQ

What is a range diagram?

A side-view drawing of the boom that relates its length, angle, radius and tip height. It shows what reach and height are possible for a configuration.

What is a working-area chart?

A top-view drawing that divides the area around the crane into zones, such as over the rear, over the side or 360 degrees. Each zone has its own capacity column in the table.

How do I find the radius from boom length and angle?

Multiply boom length by the cosine of the boom angle, ignoring boom-foot offset and deflection. For example, 60 ft at 60 degrees gives 60 × 0.5 = 30 ft. Real charts and the exam may supply radius directly, so check what the problem gives you.

Do manufacturers' charts all look the same?

No. Layout, legends and note placement differ. Since January 2023 the LAT, TLL and TSS specialty exams use a generic chart, so practice on several unfamiliar layouts and read each legend every time.