James Olszewski discovered a feature for setting the viewport scale and wanted to share it with the rest of us. 

Since forever I have been making my xref window, then zooming into my basemap to about the size needed, then.... Typing in zoom then .05xp to get one of our standard scales (because that's what someone told me to do).

When it became possible to lock the viewport scale, I made it a practice to do so as soon as practical. What I never knew -- and maybe there are others out there who have been doing the same (hate to think it's only me!) is if you don't do the zoom **.xp but instead highlight the window, right click and select "Properties" BEFORE locking the viewport display the property item for viewport scale can be clicked for a list of predetermined viewport scales to select and you can go ahead and lock it for display (if it's already locked the viewport scale property won't display a selection. This can be especially useful when getting drawings from another source where they neglected to lock the viewport display and your zooming in!

NOTES FROM CADALYST TIP PATROL:  I don’t know when this ability was first available, but it has been there for some time.  Select or activate a viewport and open the Properties Palette.  Press CTRL+1 to open it.  Under the MISC area of the properties, go to the Standard Scale option.  Click it and select the scale you want to use for the viewport.  If the scale isn’t in the list, type in the desired scale in the CUSTOM SCALE option box.  If you ever need to change, alter, or modify any object, select it and look at the properties palette.  Tested in AutoCAD 2009.