You know, there are a slew of considerations at play in all of this. Firstly, there is variance between instruments. Secondly, instruments can degrade over time. Thirdly, they should all be at the same temperature when making comparative readings, because temperature affects their performance. Fourthly, some older colorimeters may not be well-adapted to evaluating the latest generation of wide-gamut displays. Fifth, is the parameter setting done using DDC or OSD controls (can impact consistency of the test between instruments)? Sixth, turning to the software, while the internal validation of an application such as BasicColor, or ColorEyes Display is fine as far as it goes, it does not go far enough. One wants an independent application generating a completely alternative set of values to be displayed, measured and the dE calculated in order to validate "from the outside" whether the internal validation of the calibration packages is reliable. This can be done with Babelcolor's PatchTool application, which I highly recommend, having used it intensively when I had display management issues, now resolved. It's a very useful analytic application. Of course, I should add that profile quality itself is obviously a key factor in the outcomes. Generally one prefers LUT over matrix profiles for achieving more accurate results, unless the display has very linear performance.