Como
Automatically Configuring the Y-Axis Scale
You configure the trend chart to automatically scale the y-axis. The trend chart has two y-axes, one to the left and one to the right. You can use this procedure to scale both axes.
The x-axis of the trend chart represents time. The time span of the axis can be set with a fixed start and end time or with an end time relative to the present time. The axis can be quick-scaled to show the last hour, last day, last month, or last year.
The y-axis refers to the measurement unit that the variable represents. The scale of the y-axis can be set manually or by auto scale. You can configure the trend chart to present series on one y-axis or two y-axes, one to the left and one to the right. Use two y-axes to present series with different ranges in the same trend chart.
To make reading easier, grid lines can be shown in the trend chart. Grid lines can be shown in both the x- and y-direction, independent of each other.
In WorkStation, in the System Tree pane, select the trend chart you want to configure.
On the Trend Chart toolbar, click the Open trend chart settings button
.action_zoom_plus_stroke 
In the Trend Chart Settings dialog box, select Auto Scale left y-axis and Auto Scale right y-axis .
Click OK .
The y-axis scale is now set automatically and updated with the presented series.
Trend Chart Axes
Manually Configuring the Y-Axis Scale
Assigning a Series to a Y-Axis
Trend Chart Event Icons
Trend Chart Settings Dialog Box – Axes Tab
Trend Chart Does Not Show Trend Log Series