You asked for it!
For pete's sake, don't you know anything, Doug?
(Sorry, I'm jonesing without the Political Forum).
I got this from the NIST website:
(
http://www.ts.nist.gov/ts/htdocs/210/214/assessors/traceability-references/sld003.htm)
Best measurement capability [is the] Smallest uncertainty of measurement a laboratory can achieve within its scope of accreditation, when performing more-or-less routine calibrations of nearly ideal measurement standards intended to define, realize, conserve or reproduce a unit of that quantity or one or more of its values, or when performing more-or-less routine calibrations of nearly ideal measuring instruments designed for the measurement of that quantity.
Here's a nice guide from NIST on measurement uncertainty.
http://physics.nist.gov/Document/tn1297.pdf
IMO, the difference is a cal lab can attract more business or charge more by spending money to reduce their uncertainty to infinitesimal levels, whereas a test lab just needs to reduce their uncertainty to a level that gives them the capability to measure within customer specified tolerance, reducing uncertainty further does not add value.
