This class answered a question for me in that I had prepared a calendar and exported files to be printed by an outside site. to my amazement, the site replied that I did not have enough DPI.  I could not figure out why this happened.  I ended up abandoning the project, not knowing what I did wrong.  I am so glad Helen posted this class. I will now go at it again with confidence. I will use the Save for Web function and convert the DPI in Photoshop as my method of saving.  I am, however, glad to know how to do the math should I want to do that.