The X-axis, which is the horizontal axis, on most Excel charts does not use numeric intervals like the vertical Y-axis does. The X-axis contains either strings of text or a date under each set of ...

Excel automatically distributes these points along a uniform X axis. To add more data to the Y axis in a line chart, add additional numbers in cells below your existing data.

This article explains how to add a secondary axis to a chart in Excel so you can view unlike categories on the same graph. These instructions work in Excel in Microsoft 365, Excel 2021, Excel 2019 ...