Hi Mack,
That Zero to 20 thing?
Does it begin at something like 72 dpi at the printer (The Zero setting?) and then go up to 1440 or whatever the printer is capable of (the 20 Setting?)? Or something else entirely?
No, Mack. It has to do with print sharpening to fill in any loss in sharpening between what you made on the screen and what you see on the print.
The numbers allow you to adjust for paper type and ink type... it will compensate for print size all by itself. (That's why it's called Smart Sharpen. See Edit Preferences, Printing.)
Most of us start with the default 5.
You can increase the numbers if you want to, constantly being vigilant for over sharpening which can be seen as any halos around objects (easier to see if the sky is the background). Look for leaves against a sky, stuff like that.
If you work with a lot of matte paper (never played with canvas) you might kick it to an 8 and see what you get.
A 5 works for me on Epson Luster, Prem Glossy, and Ilford Smooth Gloss and Pearl.
Fred