Only in the sense of comparing to a known accurate reference.
If you have two rulers and one reads 306mm and one reads 309mm you can compare them as much as you want, but the only thing that will confirm which is closest to the correct distance is to compare one to a known accurate distance.
Yes, he's going to need access to or buy a reference. There's no way to avoid it if he wants to know which is more accurate.
I actually had the same question come up when trying to, "accurately," measure printed ink distances. In addition to the mechanical issues of print head positional accuracy and repeatability there is the variation in paper since dimensions can change slightly over time, humidity, etc.
So how accurate were my steel tapes? And how consistent?
I had a SRX1 (surveyor's total station) which can measure angles accurately to about 1 second of arc but can only measure distance accurately to about 1.5mm.
By trading off smaller angles with increased distance one can find a point where an optimal accuracy is achieved. At 15m distance the angular and distance accuracy come out to about 0.1mm expected error across a 1m tape.
I found some steel tapes had cyclical variation of about .5mm but most were surprisingly good. I took the best one, which had errors of less than about 0.2mm, and use that with a loupe to measure printed ink distance.
I haven't found anything similar that would provide a reference standard for determining color measurement accuracy. There is considerable variation amongst the 3 I1's I have in the more saturated colors. But that variation decreases as colors desaturate. All are in reasonable agreement in or near neutral colors.
On another related point, X-rite, when it swallowed GMB, added some small changes in how the GMB (I1, etc) instruments read color so the company's product lines would more closely agree with each other. XRGA I think it's called. I have found essentially no documentation on the algorithms of this change but it involved differences around 2 to 3 dE on some colors.
