I have a copy of John Neal's "All Done with Mirrors", which I read back around 2003, and as much as I enjoyed his sardonic wit at times, his Metrological Tree system built out of the roots of the two prime ratios, 441/440 and 176/175, left me feeling like he was using a scatter shot Blunderbuss approach to hitting a target instead of a high precision rifle, LOL! Not that many of the units both he and Michell discovered aren't valid, it's just that he over extended their use too much. There are two main approaches or camps dividing the study of ancient Metrology. Those who tend to regard Linear units having a functional parallel with Volumetric and Weight units, and those who just do investigations of Linear as a separate entity. I belong to the former now after years of study and seeing the same numerical factors time and again in each of those categories of ancient unit standards. I think Michell's prejudice against the modern Metric system kept him from delving too deeply into similar parallels that may have been utilized in the past in addition to his still remarkable Canonical Circ system. But I am glad you mentioned Jim Neal's book and what he had to say about certain Megalithic sites being laid out not as circles, but as elipsoids, with sometimes more than two focii points. That in itself complicates matters exponentially as far as conducting calculations on those old stone sites, as far as I am concerned. I don't think the HFC would work on those sites. Any opinions on this matter?