Mills, I got to try the new Hosford Gauge at the Spring Southern. It is really nice and requires no arbor or head changes for different guages from 28 through 10. For me the layout of its analog dial and its range give it advantages in ease of use (especially if doing multiple barrels). It is more expensive than the other tools mentioned but I really like not having to do the extra arithmetic and remember dial revolutions, etc.. HTH
http://www.hosfordco.com/sporting-sh...ore-gauge.html