Progression of symbolism in crop circles, year by year

Baktun #9, 5th Sun. Dates from +435.87 to +830.14

Below, each dot represent a crop circle of symbolic nature (see yellow table). The vertical axis (y) display the date at which each crop circle has
occured (since the 80's), and horizontal axis (x), the dates in the past corresponding to the emergence of the symbolism shown in the crop circle.

Remarkably the record of events, plotted against time, falls roughly along a straight line (in red).
This is how, emerges a linear progression of the "symbolic timeline". And this progression, given by the slope of the linear regression is
approximatively of 400 years for each real "year".

Strangely when searching for a calendar showing the emergence of symbols in human history, you will find nothing except the "13 Baktun Cycle Wave Harmonic of History" drawn by Jose Arguelles. And it fits perfectly well with this timeline. In other words, for each "real" or actual year we are advancing of 400 symbolic years, and this is precisely the time interval of one "baktun", in the mayan calendar.

Another refinement (next) ...