What is the best way of getting the COM location in a part into a usable dimension?  I know how to create a COMR point from the COM point, but I'm having trouble getting usable dimensions from it.

I'm embarrassed to say that I did this once before but now cannot figure out how.  I have a COM point and a child COMR point in the Feature Manager for this part.  (The COMR feature is below all other mass-modifying features in the part.)  Following the COMR feature I have a sketch point whose location is set by an equation such that its distance from the part origin equals "RD1@Annotations".  This seems to work and allows me to define a plane through the COMR point -- my ultimate goal -- but I can't reconstruct how I found that dimension, and in any case this seems an awkward way of going about it.  Isn't there a more straightforward way?

Related Question -- In the part describe above, the COM and COMR points don't seem to be in **exactly** the same location.  I've used the Measure Tool to locate them both individually and relatively to "high" accuracy, and they disagree by around 0.1%, even after a rebuild.  The COMR point seems to agree with the Mass Properties output, while the COM point does not.  I've even deleted the COM feature, but the COMR feature remains and continues to track the true COM of the part.  (I'm using SW Premium 2014 SP5.0)

Possibly relevant:  I don't understand the meaning of SW Help ("Example: Changing Model Geometry in Parts Containing COM and COMR Points").  In particular, what are "tab features?"

-- John Willett