I guess you are using the XY-Plot feature in ProcessBook.
The way to set the scale is in the definition dialog of the XY-Plot in ProcessBook. If you open the definition dialog (see screenshot below), you should find a scale setting on the bottom left of the dialog box. The default definition is Autorange, which means ProcessBook will adjust the scale according to the values from the tags. You can always input your desired scale.
If the tag you selected on the top is representing the X-axis, the scale that you are applying is for the X-axis. Else, you are setting the scale for the Y-axis. Do note that you can set a single or multiple scales for the Y-axis.
As mentioned by Michael in the other thread, it would really help the members of the community understand your situation and problem if you can give us more context and information. Otherwise, we would have to guess what you are trying to achieve.
Hope this helps