The one on my Bies was pretty good over the 30" range. I moved the tube to the right to get some extra capacity out of it. I added a Rockler tape as a replacement. It is off about 1/16" in 18" or so; really poor in my opinion.
I added the Wixey digital gauge which is great and the current tape gets me close enough to fine tune my measurement in with the DRO. I still want to add an accurate tape because I'm just that way ;-) Many folks have talked about the Starrett so I will probably go that way.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke