A secondary vertical axis can display series with different units, but two adjustable scales can also make unrelated trends appear closely aligned. Label both scales clearly.
Confirm a supported chart
Google documents a second Y-axis for line, area, and column charts. Double-click the chart and check its type and data series before looking for an axis assignment.
Verify the underlying units. Revenue and margin, for example, may need different scales, while two revenue series usually need directly comparable treatment unless another reason is explicit.
Assign the intended series
Open Customize > Series, select the series under Apply to, and choose Right axis. Then inspect the Right vertical axis settings.
Add meaningful left and right axis titles and number formats. Confirm that the intended series moved rather than another similarly named one. Google does not offer a second X-axis through this setting.
Review the interpretation
Compare known values with each axis and check minimum and maximum settings. Avoid adjusting bounds solely to make lines overlap. Include zero where the chart and comparison require it, and explain any deliberate truncated scale.
Check the chart at the size it will be shared, including a phone or exported PDF. Readers should be able to tell which line uses which units without guessing from color alone. Consider separate aligned charts if the dual-axis version encourages a misleading visual comparison. A secondary axis solves a display-scale problem; it does not establish correlation, causation, or a valid combined measure between two series. Keep the underlying period consistent across both measures.
References
Reviewed against the linked official product guidance on November 3, 2026. Features, limits, screen labels, and access can vary by account, platform, region, and organization policy.