The caliper Addon allows you to add meausurements directly in Blender.
The new version for Blender 2.6 allows updating the caliper automaticaly, which is awesome. But the use is still a little bit tricky. So I hope this video helps you getting it.
You can find the addon here: macouno.com/2012/05/08/caliper-for-blender-26x/
Loading more stuff…
Hmm…it looks like things are taking a while to load. Try again?