Thank you very much for all your effort.  A very unique and free learning opportunity for any of us willing to take advantage of it.
I believe I asked you this once before, but I am still confused on the term frequency .  My definition would be something that recurs with regular periodicity, in either x or y axis, or perhaps along the sloping line in this case.  The lines you have indicated as frequency, don't seem to follow that logic, being parallel to the fork and of unequal length and distribution, at least to my eye.  Is this just a term specific to forks, with a unique meaning, or is there more to the frequency that just isn't indicated on the charts.