Mike, I used a test indicator simply because they are easier to setup and you can get down closer to the center line of the blade, (travel indicators have to be held pretty much perpendicular to the surface that you are checking). Test indicators are also more expensive than the travel type: The Swiss made Interapid that I showed in the pictorial has .0005 resolution and retails for around $235 these days.
You can purchase a Starrett “Last Word” test indicator (sufficient, but not great) for around $100. http://www.mytoolstore.com/starrett/test04.html
Michael, I suspect that both of the miter slots are typically machined at the same time, and therefore should be parallel to each other.
Kent, MSC sells the industrial versions but I think the Grizzly would be satisfactory.
MSC:
http://www1.mscdirect.com/CGI/N2DRVSH?SISHNO=957274&SISRCH=1&SIS0NO=208108&SIT4N O=5354898&SIOR=2
Grizzly Surface Gauge:
http://www.grizzly.com/products/h2713
Grizzly Test & Travel indicators: (Keep in mind, you do not want the .0001 resolution, they are way too sensative for this application)
http://www.grizzly.com/products/searchresults.aspx?q=dial+indicator&submit.x=5&sub mit.y=11
As you can see by the pics below, a travel type indicator will do the job almost as well.