Great question and one that I wish I could go in to extreme detail on how it is done because X-Rite has truly came up with a very advanced way of calibrating the D3 family. We are under NDA with X-Rite for much of the details but I will try and cover as much as I can without violating that.
We started working with X-Rite just about two years ago on what is now the D3 family. We went to the design team at X-Rite and had meetings with their color scientist team including some of the guys from the original Sequel Imaging group. We had a long laundry list of requests we felt the industry was going to need in the near future as display technologies were changing so fast. Some of those requests were: The ability to read at very low light with repeatable results because displays and projectors are getting so dark. The meter needed to have a tripod mount embedded in its body because displays are getting much bigger and hanging the meter cord over the top of the display is not a good option anymore. Accessories or components that can’t be lost or misplaced like with the D2 and C5 so a attached diffuser with detector to tell us if it is properly in place. A design that dealt with highly polarized and angular light that LCD manufacturers seem to be doing to focus more light into a narrow vertical but wider horizontal viewing area. Sealed optics and sensors to minimize drift over time. The ability to add display characterization data to the meter in the field to help make the meter future proof over a longer period of time.
What are the two things that make a meter obsolete? Sensor drift over time and display technology changes. Both of these problems are interrelated. You need a very stable and accurate filter array to solve the drift over time issue and once that was solved you can take advantage of it. With a stable and accurate filter/sensor array you can characterize each meter at the factory with a high degree of accuracy.
The second issue that can make a meter obsolete is changing display technology specifically the spectral response curve. Here is an example of a spectrum sweep with the 1931 2 deg standard observer curve on it.
A tristimulus meter through its filters and sensors try’s to mimic the standard observer curve in this case the 1931 2 deg CMF. Which if all display spectral response curves match the 1931 2 deg observer and the filters in the meter did the same we would not need to calibrate or characterize the meter. But in real life the meters filters are never perfect and have deviations. I have not seen a display that perfectly matches the 1931 2 deg standard observer. So in the past we had to create a calibration table for each major type of spectral response curve to cover our bases. As part of that processes of creating additional tables for each spectral response curve it also took into account the deviation in the meters filters. This is how it’s been done for a very long time and is the recommend method by NIST for calibrating a tristimulus device. But now that X-Rite has eliminated the need to deal with the filter/sensor deviation we can solely concentrate on just the display spectral response not matching the standard observer curve. So with a highly stable and factory characterized meter and the ability to add display characterization data outside the factory you have a field upgradable tristimulus meter.
As part of the work with X-Rite we worked out a deal to be able to provide these field upgrades with the SpectraCal C6. Our inhouse lab that does all of this work is quite extensive starting with our Konica Minolta CS-2000 which is only one of two devices certified by X-Rite for this work the other being a CS-1000. The lab is temperature and humidity controlled. Each display device has went through a very rigorous process of testing before being used in the lab and is calibrated before each meter or research run. The mechanical jigs used to line everything up for calibration or testing is controlling tolerance down to or even some times under 1mm.
I hope this helps everyone out and I wish I could go into a lot more detail because it is really very cool color science X-Rite really did their homework.