Select the plot to which the other plots should be synchronized and click the 
button on the Scale toolbar.
The Plot Synchronization function provides a quick method for setting the time period of all the plots to be the same as the active plot.
Plot synchronization can be applied by four methods:
From the Plot menu, select Scale and Synchronize Plots. All plots will be synchronized to the active plot.
OR
Right-Click on the Plot to which the other plots should be synchronized and then click Synchronize Plots.
OR
Select the plot to which the other plots should be synchronized and then use the Ctrl-Z hot key.
OR
Select the plot to which the other plots should be synchronized and click the button on the Scale toolbar.
Note: It the active plot is off-line, then all other plots will be automatically switched off-line when they are synchronized to it.
Tip: Since Plot Synchronization sets the time period for all plots to be the same, it allows comparisons to be made between items that are being trended in different plot windows.
In addition to user initiated synchronization stPro can be configured so that all of the plots within a single session will always remain synchronized. When in this mode, any changes to the plot duration, start-time, end-time or scan status of the lead plot will be applied to all other plots within the active session.
To activate this feature check the "Always Synchronize Plots" option on the User Preferences Plot tab.
Note: When enabled, the plot right-click "Synchronize" option will be pre-fixed with a tick and will be disabled to indicate that the plots will always be synchronized. The Synchronize Plots (Ctrl-Z) toolbar icon will also be disabled to further reinforce that manual plot synchronization is hot required.