This question is prompted by another round-robin type study involving the calibration of thread plug gages, the results of which were predictable because similar studies over the past twenty years or so have produced similar results.
Some years ago I wrote about the ‘digital disease’ and how too many people actually believed digital displays with millionths of an inch resolution when the device they were part of could not deliver results worthy of the last few digits.
Some folks select the calibration source based on convenience. They reason that the best choice for them is the lab down the street or around the corner because they don’t have to ship their stuff any distance to get it done.