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Pete,
A great picture! Keep at it.
Getting a precise gray scale setting is difficult without a color meter, but IF the bias and drive controls do not interact too badly you can usually get a pretty good result by eyeball. It really helps if the controls can be rocked back and forth through the correct point - you can go for decreasingly obvious misadjustment as you rock the control back and forth, and zero in on a good point. The ideal is to be able to set the lowlights and the highlights separately, doing the blacks/dark bars first - but not all sets will let you do this. Looking at the CT-100 schematic, if the DC clamping is working OK, you should be able to set the lowlights close and then set the drives for proper white. Then touch up the lowlights for precise tracking, and go back and forth from highlights to lowlights again if necessary.
Because of differences in phosphor spectra, a filter colorimeter may be slightly off in its readings. The Zenith optics lab had to use a master spectroradiometer to calibrate filter-type colorimeters to the current phosphor set - the colorimeters would then have a multi-positon switch for different calibrations. The spectroradiometer was calibrated against a NBS traceable standard lamp, and then the color was calculated from the measured spectrum using the CIE standard obsrerver curves. (These curves have been shown to have some errors, but that's another story). I believe that nowadays there are better ways to calibrate than a standard lamp, using power measurements of laser sources, but I haven't kept track of what optical instrument companies are actually doing.
The best white point setting (for one observer) can be made using a split-screen D65 lamp. This device has a window that is half open to the CRT and half mirrored to reflect the D65 lamp. The view is of the screen gray bar immediately adjacent to the lamp gray, with no intervening frame line. Any one person can get a near perfect match (for him/her self) of monitors having any phosphors by using this. However, other individuals likely will see the match as slightly off due to normal color vision variations. I and one of the older engineers always disagreed on how much blue drive produced a match. (He needed more blue.) Now that I am older and slowly developing cataracts, I probably need more blue than I used to.
The colorimeter substitutes its filtered spectral responses for the human eye, which is reasonable but not as accurate as a spectroradiometer, hence the need for multiple calibrations depending on the phosphor characteristics. I would guess that the colorimeter will be fairly correct for the different greens, both of which have smooth spectra, but may show errors due to the difference between the CT-100 red spectrum and the spikey rare-earth red spectrum of a modern tube.
So - if you get a colorimeter, and the two sets don't end up looking like the same gray scale, you may have to trust your eyes.
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