IGCSE ICT 0417 - Graphs and Charts

16. Adding a Second Axis

This section explains how to add a second axis to a graph or chart in spreadsheet software like Microsoft Excel or Google Sheets. Adding a second axis is useful when you want to display two different sets of data with different units on the same graph, particularly when one set of data has a significantly different scale than the other. This allows for a clearer visual representation of the relationship between the two datasets.

When to Use a Second Axis

Consider using a second axis when:

• One dataset has a very large range of values compared to the other.
• You want to emphasize a trend in one dataset that might be obscured by the other.
• You are comparing two datasets with different units (e.g., temperature in Celsius and Fahrenheit).

Adding a Second Axis in Spreadsheet Software (Example using Excel/Google Sheets)

1. Select the data series you want to add a second axis to.
2. Right-click on the selected data series.
3. Choose "Format Data Series..." (Excel) or "Format Series..." (Google Sheets).
4. In the "Format Data Series" pane, go to the "Series Options" tab.
5. Check the box next to "Secondary Axis".

Understanding the Second Axis

When you add a second axis, the software will create a new vertical axis on the right side of the chart. This axis will be scaled independently of the primary axis. You can customize the appearance of the second axis, including its title, scale, and number format.

Example Scenario

Imagine you are plotting the temperature of a liquid in Celsius and Fahrenheit on the same graph. The Celsius temperature might range from 0°C to 100°C, while the Fahrenheit temperature might range from 32°F to 212°F. If you plot both on the same primary axis, the Celsius data would appear as a flat line. Adding a second axis allows you to display the Fahrenheit data on a separate scale, providing a clear visual representation of both temperatures.

Table: Key Considerations for Second Axes

Consideration	Description
Scale	Ensure the scale of the second axis is appropriate for the data being displayed.
Title	Provide a clear and descriptive title for the second axis.
Number Format	Use appropriate number formats for both axes to ensure clarity.
Clarity	Ensure the graph remains clear and easy to understand with the addition of the second axis. Avoid clutter.

Practice

Practice adding a second axis to various datasets in spreadsheet software to become comfortable with the process. Experiment with different scales and titles to optimize the visual representation of your data.