I completely agree about color measurement devices. I was attempting to comprehend the purpose and actual usefulness of SID in a LAB world. It seems that the conclusion is that SID seems to be a necessary evil as a launching point. Is that a fair point?
I don't think that's a fair point. I don't think SIDs are a necessary evil. SIDs and Lab are two different metrics that have their place. I have the feeling that you've never run a press.
The press operator adjusts SIDs and that affects ink film thickness which in turn affects Lab values.
In the G7 How to Guide there is this statement which acknowledges this point: "If the 50c, 40m, 40y gray balance patch varies from the ideal Lab values, try adjusting CMY solid ink densities (SID) within permitted tolerances to achieve the ideal CIELab gray value(s)."
The important thing in that statement is that it references that SIDs have permitted tolerances. That is because of the fact that the press, as I wrote earlier, is a mechanism for delivering a film of ink on to a substrate. There is a minimum and a maximum ink film thickness within which the press can operate in a reliable manner. Exceed those limits and the process will no longer work irrespective of whether you hit the Lab values or not.
The press operator needs to know the center point for his ink film thickness as well as the upper and lower limits. That's what he uses a densitometer to measure. In that sense the press operator is not trying to make color (the Lab values) on the press. In a well run shop a press operator can run the press up to their center point SIDs and even without a proof will be very close to final color. In fact that is what is done in many magazine publication printing today. They run to the SID numbers and get the correct color because the press has been set up to hit ISO 12647-2.
Another quote from the G7 guide: "The good news is that densitometric press control is still quite valid (even recommended) once the optimum density values for a particular combination of ink, paper and measuring instrument have been determined. Printing to these solid values while also measuring the CMY densities of the mid-tone gray patch (HR) will produce equally good results as CIELab measurements, but is more intuitive to experienced press operators."