What is Sync Axis in Tableau?

Building a chart in Tableau is a great first step, but making it tell an accurate and truthful story is the real goal. One of the most common ways visualizations can become misleading, even accidentally, is with a dual-axis chart where the two axes aren't aligned. This article will show you exactly how to use Tableau's "Synchronize Axis" feature to keep your charts honest and easy to understand.

First, What Are Dual-Axis Charts?

Before we can synchronize an axis, we need a chart that has two of them. In Tableau, a dual-axis chart allows you to compare two different measures against the same dimension. It's an incredibly useful technique for layering multiple types of data onto a single visualization.

A classic example is comparing Sales and Profit over a period of time. You might want to represent Sales as bars and Profit as a line on the same chart. This tells a much richer story than looking at two separate charts. You can see at a glance how profit trends with sales - do they rise and fall together, or are there months with high sales but low profit?

To create one, you typically drag a dimension like Order Date to the Columns shelf, then drag your first measure (e.g., Sales) to Rows. Then, you drag your second measure (e.g., Profit) to the Rows shelf as well. Tableau will initially create two separate charts stacked vertically. To combine them, you right-click the green pill for your second measure on the Rows shelf and select "Dual Axis."

And just like that, you have one chart with a left and right Y-axis, one for each measure. This is where the potential for misinterpretation begins.

The Danger of Unsynchronized Axes

When you first create a dual-axis chart, Tableau’s default behavior is for each axis to operate independently. Both axes automatically adjust their scale to best fit the range of values for their respective measure. While this sounds helpful, it can create a deceptive picture.

Imagine your company's Sales for the year range from $2.0M to $4.5M. Your Profit, meanwhile, ranges from $200k to $450k. The scale for sales is roughly ten times larger than the scale for profit.

On an unsynchronized dual-axis chart:

• The Sales axis might range from $0 to $5.0M.
• The Profit axis might independently adjust its scale to range from $0 to $500k.

Visually, a month with $400k in profit would appear just as high on the chart as a month with $4.0M in sales, because each value is near the top of its respective axis. Your profit line might look like it's soaring high, closely shadowing your impressive sales figures. This can lead stakeholders to believe that profit margins are incredible when, in reality, the profit is only a fraction of the sales revenue.

The visual relationship doesn't match the actual numerical relationship, and that’s a big problem. You can't accurately answer questions like "Is our profit greater than half our sales this month?" just by looking at the chart. This is the exact issue that Synchronize Axis is designed to fix.

What Exactly Does "Synchronize Axis" Do?

The "Synchronize Axis" command in Tableau does one simple but powerful thing: it forces both axes in a dual-axis chart to use the exact same scale.

When you click it, Tableau looks at the data ranges of both measures you're plotting. It then finds the minimum and maximum values across all the data and creates a single, unified scale that can accommodate every data point. Both the left and right axes will now display the exact same numbers, from the same lowest to the same highest value.

Revisiting our Sales and Profit example, if you synchronize the axes, both will now likely display a range from $0 to $5.0M. The Sales bars will remain large, filling up a good portion of the chart. The Profit line, however, will now appear much lower, clustered near the bottom of the chart. This is a far more accurate representation of reality. It instantly conveys that while profit is great, it’s a much smaller figure than the total sales revenue.

Essentially, synchronizing the axis turns a potentially misleading comparison into a true apples-to-apples view, ensuring that the visual proportions of your marks directly reflect their numerical proportions.

How to Synchronize an Axis Step-by-Step

Putting this into practice is incredibly simple. Let's walk through it using the Sales vs. Profit example with the "Sample - Superstore" dataset that comes with Tableau.

Step 1: Create Your Dual-Axis Chart

1. Drag the Order Date dimension to the Columns shelf. You might want to right-click it and choose "Month" for a better view.
2. Drag the Sales measure to the Rows shelf. Tableau will create a line chart.
3. On the Marks card for SUM(Sales), you can change the mark type to Bar.
4. Drag the Profit measure to the Rows and drop it right next to SUM(Sales). You now have two separate charts.
5. Right-click the SUM(Profit) pill on your Rows shelf and select Dual Axis from the menu.

Your charts are now combined. You'll see bars for Sales and probably circles or a line for Profit overlaid, with one axis on the left (Sales) and another on the right (Profit).

Step 2: Spot the Different Scales

Pause here and look closely at your chart. Notice the left axis for Sales goes up much higher (e.g., to $140,000) than the right axis for Profit (e.g., to $25,000). This is the unsynchronized state we talked about.

Step 3: Apply Synchronization

This is the magic step. All you have to do is:

1. Move your cursor over one of the axes on your chart - for instance, the right axis for Profit.
2. Right-click directly on the axis. A context menu will appear.
3. In this menu, simply find and click "Synchronize Axis".

That's it! Instantly, you’ll see the right axis scale jump up to match the left axis. The marks on your chart will resize and reposition themselves to reflect their true values on this new, unified scale. Your profit line now accurately reflects its value relative to sales.

Tips, Tricks, and Troubleshooting

While the process is straightforward, you might run into a few common scenarios. Here's how to handle them.

What if "Synchronize Axis" is Grayed Out?

This is a common frustration, and it almost always happens for one reason: your measures have different data types. Tableau can only synchronize axes for measures that share the same data type. For example, it can't create a unified scale between an integer (Number (whole)) and a decimal (Number (decimal)), let alone a number and a string measurement.

The Fix: In your Data pane (on the left side of your screen), check the data types of both measures. They're shown by the icons next to their names (e.g., # for a number, Abc for a string). If they don't match, right-click on one of the measures, hover over "Change Data Type," and change it to match the other. After aligning the data types, the "Synchronize Axis" option should become available.

Cleaning Up Your Chart by Hiding the Redundant Axis

Once your axes are synchronized, they display the exact same information. Keeping both of them on the chart is redundant and adds unnecessary clutter. It’s best practice to hide one to simplify the view for your audience.

The Fix: Right-click on the axis header you want to remove (typically the one on the right), and simply uncheck the "Show Header" option. The axis will disappear, but your data will remain perfectly plotted on the single, shared scale. Don't worry, the dual-axis functionality is still active.

Knowing When Not to Synchronize

Synchronizing is critical for comparing measures of the same unit (like dollars vs. dollars). But sometimes, you want to compare two metrics with wildly different scales just to see if their trends and patterns are similar. Consider comparing:

• Website Sessions (in the millions).
• Conversion Rate (a percentage between 0-5%).

If you sync the axes here, the numbers in the millions will force the tiny percentage values into a nearly flat line along the bottom of the chart, making it impossible to see any trends in your conversion rate. In cases like this, it's actually better not to synchronize the axes. Your goal is to see if conversion rate spikes when traffic spikes, not to directly compare the numerical value of "1 million sessions" to "2.5%". Just be sure to label your axes clearly so your audience isn't misled.

Final Thoughts

Perfecting the dual-axis chart with synchronized axes is a mark of a thoughtful analyst. It ensures your visualizations are not only visually appealing but also statistically honest, allowing for clear and accurate comparisons that drive better decision-making.

As powerful as tools like Tableau are, there's always a manual process of building, formatting, and refining charts - like finding and clicking the Synchronize Axis option. At Graphed, we automate away that busy work. Rather than dragging pills, right-clicking menus, and formatting charts, you can simply ask a question in plain English, like "Show me a chart of sales vs profit over time on a synchronized axis," and get a perfect visualization in seconds. This lets you spend your time exploring data and finding insights, not wrestling with chart settings.