Larry:
The gauge is kinda cool; as Steve pointed out, it only reaches 6 inches or so, which is plenty for checking chokes or chambers; I think the accepted measurement for bore diameter is 9" from the breech face, so this is a bit lacking for that exact measurement. Overall, though, not too bad, although you do need to develop a sense of "feel" for when to take your measurement, as the longer rods are a bit willowy when forced against the choke or chamber walls.
Craig