# To use axis in a chart

An axis is part of a coordinate system, which is a system of two or more lines, positioned at right angles, which define one or more points on a plane. In mathematics, an x, y, and z axis are used. The Chart Manager has four axes:

- Category axis as x-axis
- Data axis as y-axis
- Series axis as z-axis
- Data axis II as (second) y-axis

Three axes are required to draw a graph:

- The series axis
- The category axis
- The data axis

The data axis II is used if two (or more) different series must be drawn to a different scale in one graph for comparison.

The axes of a vertical graph are placed as follows:

Category axis (x-axis): | horizontal |

Data axis (y-axis): | vertical, left |

Data II axis: | vertical, right |

Series axis (z-axis): | horizontal, right (3-D only) |

The category axis (horizontal axis) can intersect the data axes at any point; the intersection is defined in the Axis Data (ttchm3130s000) session on the Data menu. In a horizontal graph the data axis is positioned below and the data axis II above; the series axis is on the right and the category axis is on the left-hand side.

The attributes must always be filled, even if the axes are not visible, as the data is always placed in a (fictive) coordinate system.