AKC STANDARD:

Clarification: The tail is another very distinctive Pug characteristic. It must be set well up on the back. A double curl is perfect, but a tight single or 11/2 twist should not be faulted. Although the Standard states that the tail be carried over the hip, it is now generally accepted that it may be carried on top of the back as well.

Undesirable: A floppy, loose curl not carried tight to the body; less than a single curl: low tail set; tail too thin; tail carried uncurled.

Set high and tight to body	Double curl but low set
Moderately low set but tight to body	Low set and carried loose