I appreciate your situation but I can't help but remember the line from Star Wars # 4 (The New Hope). "Who is more foolish? The fool or the one who follows the fool?"
From my own research, I seem to have come to the conclusion that this confusion began when AVSHD-709 test disc came out. The test material seems to be okay but the documentation is sorely lacking. Upon researching the origin of the test material, it seems that two main individuals were instrumental in it's creation. The original intent was to provide a "no cost" test disc for the masses but the problem arises when it came down to the documentation. They were not technical writers and neither did the get the documentation proof read. They too seemed to appear to lack the necessary technical back ground to know what the standards should be or how to achieve it. Before this test disc came out, there was no real reference of debates as to how to set contrast and brightness.
The 240 limit seemed to possibly come from two sources. One, is based on Mark Sydow (the creator of the test material in question), who in my opinion may not be fully clear on the standards as well. In a forum entry he stated that he liked to set his settings at 240. The second is the possible confusion with the chroma limits (which can go as high as 240). An individual from SpectracCal based his rebuttal on this fact for the setting of contrast & brightness which only left me with the conclusion that he needed to do more research.
At the risk of Dominic Chan accusing me of lecturing everyone, I will state the whole secret of brightness & contrast is to understand the basic anatomy of a video signal and how to read a waveform monitor. In this case Luma is the key.
Black = 0.0007Mv. (Absolute 0 Mv. is reserved for the blanking function for the horizontal/vertical sync). White = 700 mv.
0 % or 0 IRE (Confusion exists between IRE and Percentages; essentially they are the same). 100 % or IRE
In a Rec BT-709 settings and under broadcast legal standards any possible video signal regarding Luma above 235 will be truncated and therefore adjusting a display to show anything possible Luma from 236~254 is of no value. The process of diminishing the contrast setting so that bars can be seen only serves to ****** the contrast ratio.
To help you, there are a number of tutorials on how to read a waveform monitor on the web. I have attached two links that address everything on setting up contrast and brightness from those who create the standards. The documents are from UTI.
BT-814-2 and
BT-815.
There is so much to say on the subject that volumes could be written but the individuals like Dominic Chan would have bases for their rants.
In my younger years I was told this bit of wisdom that gave some situations clarity, "In some cases the only difference between a professional and a amateur is one gets paid".
Strive to educate yourself all the time. Knowledge and experience will allow you to see the truth; where others do not.
Calibration is the act of measuring, comparing and adjusting to a known standard. If one decides to make and adjustment to not comply to the known standards then it is not a true calibration but a personal tweaking.
I wish I had the time, as there is so much more to say.