Sometimes a Ruler Guide Just Doesn't Measure Up
It’s easy to create Guides. Just click on the Vertical or Horizontal Rulers and drag a Guide onto the page. But Ruler Guides have their limitations. They can only be straight and perfectly vertical or horizontal. So what if you need a diagonal, or curved Guide or a Guide that’s a closed Path?
The good news is Ruler Guides are not the only way to create Guides in Illustrator. Any simple open or closed Path can be made into a Guide. Just select a Path and go to View > Guides > Make Guide and the Path will become a Guide.
Tip provided by Jeff Witchel, Certified Adobe® Training Provider.