The axis is the measuring scale that is typically placed towards the left and bottom of your chart. Normally, the axis on the left is called the Primary Vertical Axis and the axis placed at the bottom is called the Primary Horizontal Axis. Two more axes can be placed for most chart types — these would be the Secondary Vertical Axis towards the right side of the chart’s Plot Area, and the Secondary Horizontal Axis above the chart. In common everyday usage, both the Horizontal axes may be called the X axes, and the Vertical axes may be called the Y axes. Additionally, the Horizontal axes are also called Category axes, and the Vertical axes are sometimes called Value axes. In addition to X and Y axes, some chart types such as 3D charts can also have a Z Axis — known within the PowerPoint interface as a Depth Axis. Commonly this may sometimes be called the Series axes.
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