I don't know if a digital tube mic with a 60* spindle is available but there are other fixtures that will do the same thing, this one for instance...
http://www.sinclairintl.com/reloadin...prod39927.aspx
I guess it mostly depends what one prefers to use and the price. Either one allows you to measure accurately all the way to the shoulder. When I turn necks I just barely nick the shoulders, maybe a .001" or so.
http://i60.tinypic.com/3088hsy.jpg
Using a mic or indicator with a 60* anvil allows measuring all the way to that cut.
With that said, I only have a few with tight necked chambers. My 250Imp for instance is a .283" so I need to turn the brass with bullets seated to .281". For the rest "if" I turn its only maybe 50-70%, just enough to knock off the thicker portions and true them up a little. Other than that I don't waste my time.
Bill