You need to scale the math channel in the 'Edit' window of the 'Math channels' menu option.
First of all, if the Math channel is in an existing Library (not one you created) you will have to create a duplicate to be able to edit it. Then just do the following:
Go to Edit->Next->Next to get to the range and units window.
Set the Units to be used for the scaling by entering the acronym that you would like to see on the scale for the units in the 'Short Name' box, and then enter the full name of the of the units in the 'Long name' box.
Tick the 'Override automatic range selection.' option under Range, set the maximum & minimum values for the range to be displayed at the top and bottom of the scale.
Click Next->Finish to complete the change.