What is the problem that (monitor) calibration tries to solve? I would guess "the fact that the precise perseptual response for a given display input is unknown, and for some applications, e.g. image editing, there is a need to know what the user is seeing". The reason why it is unknown is because display manufacturers generally do not share the ideal/new response of their products in a machine-readable format, and because 2 identical, new displays may have somewhat different response, a third identical display may have another response after years of (ab)use, and a "cold" display may differ from a "warmed up" display. If we had an instrument that correlated perfectly with human visual system, it would be easy. Connect it, calculate the error, and feed back some correction. Such instruments do not exist. I am a bit lost when you say that a single monitor+colorimeter correction matrix can be used to correct future measurements. How can one know that the "unknown stuff" that makes monitors/colorimeters change over time and over production runs, does not also make this correction invalid? Are there known knowns and known unknowns?:-) May one assume that the spectral response of each primary is constant (and can be baked into a correction matrix), while the flat gain of each primary is fluctuating and should be calibrated every once and again using a colorimeter and correction matrix? Thank you for your time enlightening me -k