What is a Gauge Chart?
A gauge chart looks like a speedometer and shows one measure of performance against a goal. It uses elements of a pie or donut chart and a pointer to indicate where a value currently stands. Often called dial charts, they consist of a semicircle that is colored in to represent milestones, and a dial that points to the end result.
Gauge charts are an excellent visual tool that easily communicates one item of information in a clear way such as a body mass index chart. The bottom of the scale starts at 14, and the top finishes at 34. The scale has four colors: blue for 14-19 “low,” green for 19-24 “good,” orange for 24-29 “overweight,” and 29-34 red for “obese.” An individual’s score can be plotted with the needle pointing to their body mass index number.
Gauge charts are often used in business intelligence visualizations. They communicate information clearly, even to non-experts or those not familiar with the business. They often are included on business dashboards, as a reminder of continuing key performance indicators.
When Should a Gauge Chart Be Used?
A gauge chart is a simple chart but has a strong set of criteria on its use:
- Can only measuring one thing
- Must start at 0 unless there is a pressing reason not to
- Must be linear
- Shows a single percentage of achievement
Ideal uses for a gauge chart could include anything with a goal or target:
- Work completed against a total volume of work
- Sales completed vs the sales target
- Profit compared to the budgeted goal
- In project management, to define deadlines and modules
- In economics and finance, to show researched details and statistics
- Performance of a team against measurable key performance indicators
- In academics, analysis, HR, and healthcare, to show key indicators
In a business setting, sales data is an ideal example. A business target for annual sales is set at $1 million. The gauge chart starts at $0 and finishes at $1,000,000. The scale is divided into thirds in red, orange, and green. The year-end sales reach is plotted with the needle pointing at that number. This immediately shows where an organization sits in terms of their sales target.
Best Practices for Gauge Charts
Because these charts are so simple, there are very few rules or options that can be changed. Choosing the colors of the semicircle are important, especially where the colors change. For instance, if a team measures sales volume, the first third could be red (signifying low performance), the second third as yellow (signifying normal or acceptable performance), and finally the last third as green (signifying high performance).
The gauge must always start at zero unless there is a very good reason not to—such as a BMI because no one can survive with a zero BMI. If the measurement is a percentage, it should finish at 100 percent, but if it is a value, there’s no set limit.
Advantages of Gauge Charts
Simple and Easily Understood
Gauge charts only measure one thing and present this information like a speedometer. Values are easily differentiated using color-coding, which is intuitive and immediately interpreted.
Disadvantages of Gauge Charts
A gauge chart only shows big data points on a big area. Other charts show finer levels of detail. A gauge chart is a broad brushstroke.
Because the chart shows no context, there is no extra information, so the graph could be misleading. For instance, if the gauge shows total sales for the year, and the needle is in the first quadrant, it could look like the store has performed poorly. However, if it is showing the results after two months of the financial year, or for one store out of ten, there is a lack of context.
Can Be a Waste of Space
Sometimes multiple gauge charts are used when a single bar or other chart style would be better.
Not Accessible to All
Because gauge charts use color to communicate information, they are not color-blind friendly. A large proportion of color blindness is in red and green, making the “traffic light” colors inappropriate. A significant portion of the population is colorblind, so companies should caution themselves on the colors they choose.
A Business is Not a Fighter Jet
A gauge in a fighter jet is all you need to display the speed, elevation, or air pressure, as these are single measures that are important. Conversely, a business needs context, relationships, history, and other values. It is very rare that one single measure or value can be helpful when viewed alone.
Alternatives Instead of Gauge Charts
Bullet charts are a variation on bar charts. Stephen Few developed these as a replacement for gauge charts, noting that they saved space and were color-blindness friendly. Simply, they look like thermometers, which can be horizontal or vertical. There are gradients of “success” in grayscale, and then a darker bar in the middle. indicating where the measure has reached. These are an excellent replacement for gauge charts—with an added bonus of smaller color gradients and sideways measurements.
Advanced Gauge Chart
In an advanced gauge chart, more than one needle can be plotted onto a single gauge. This is ideal where there is a single thing being measured but a number of categories. For instance, if a chain of electronic stores have the same sales target but are all achieving different amounts, these can be plotted with different needles. However, this is only effective when there is sufficient distance between the needles for clear viewing.
A simple line chart is a better choice than a gauge chart if the data is shown over time, rather than a single value. Line charts are easily understood and can present more complex data.
Bar or Column Graphs
If there are multiple measures, a bar or column graph is far more appropriate. These easily show multiple measurements like the sales achieved by multiple branches of electronics stores. There is no risk of losing data with multiple needles. They also take up less space than multiple bullet or gauge charts.
Donut and Pie Graphs
Pie and donut charts, while similar in shape and appearance, are completely different to gauge charts. They are related to non-quantitative data and how a whole can be divided up into individual parts.
Future of Gauge Charts
While gauge charts look great in reports, bullet charts may be a better option. They save space and are easier for readers to interpret. Consider a bar or column graph if there are several measures to provide extra context for readers.
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