Saving and Using Spatial Bookmarks
ArcGIS has the ability to set a 'spatial bookmark.' These bookmarks record both the scale and extent of the data. Using bookmarks allows you to zoom and pan as you wish, and then return to a particular map location (e.g., for a map layout or specific area of interest). A .mxd can have multiple bookmarks.
In the data or layout view, you can set the Map Scale as desired.
For example, you might wish to have a map, set at 1:120,000, and panned so as to include the Bellingham city limits:
To save this extent/scale, choose Bookmarks from the View menu, and click on Create...
Enter a Name for your bookmark as desired and click OK
Now, you can Zoom as you like...
...or Pan around...
Then, to return to you bookmarked location, choose Bookmarks from the View menu again, and select your bookmark
Note that both the extent and the scale are returned to via the Bookmark