If we look, then, at the first example from 9 November 1969—actually sent, or at least postmarked, on the very day of Stine’s shooting in Presidio Heights—we can see clear indication that The Zodiac conceived a method of communication of some information that required the circle of his symbol to be marked off with 12 equally spaced points, 4 of these formed from the cross itself, and 8 interpolated. What is further evident, however, is that, whatever it is he is marking out here, he does not appear to be interested in conveying any further interpolations. All of the five marked crosses fall on one or other of these 12 points and not in between.

This point alone indicates that we are not to visualise the circle of The Zodiac symbol as presenting any kind of continuous line or scale used for mapping, but rather as merely a medium for plotting against 12 differentiated and discrete points. There is no consideration, and therefore no implied meaning, to any ‘in-between’ points.

This observation alone will help us when we come to the next part, which is to consider what it may actually be that he is plotting for us in this manner.

The general interpretation to be presented next is, to date, a well-discussed one, presented, however, with some additional speculations.

On the door of Hartnell’s car at Lake Berryessa The Zodiac had written the dates of his first two hits, together with the one he had just committed. 

We are going to pull out and be focussing on the specific months in which each of these occurre, to which we add the most recent shooting to give us:

• December;
• July;
• September;
• November,

given which we can conceive of the figure as documenting this sequence of months visually, together with one tantalising, perhaps spurious, addition.

Posted by: @shaqmeister

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If we look, then, at the first example from 9 November 1969—actually sent, or at least postmarked, on the very day of Stine’s shooting in Presidio Heights

CORRECTION: Stine was actually shot on 11 October 1969, and the Zodiac did send a letter on this date, but it was not this one.

Posted by: @shaqmeister

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We are going to pull out and be focussing on the specific months in which each of these occurred, to which we add the most recent shooting to give us:

• December;
• July;
• September;
• November October.

CORRECTION: as previous.

This interpretation is, however, only possible if, together with the point made about there being only 12 discrete points to plot against, we accept the following as also inherent in the construction of the figure:

1. that the direction of the sequence of months projected in this manner goes counterclockwise; and
2. that the origin of the sequence of months, if we take this conventionally to be January, does not sit at one of the cardinal points of the figure, but off to one side.

Both of these appear odd and, perhaps, counterintuitive initially. However, some of this uneasiness can easily be dispelled through asking what the significance, if any, of the four cardinal points could be otherwise. What occurs, consistent with this choice of association, in the months of December, March, June and September?

To those in the know, of course, in June and December we have the Summer and Winter Solstices, respectively, whilst in September and March we find the Autumnal and Vernal Equinoxes. And these, plotted on a reduced down schematic of the celestial zodiac, would be rendered precisely in this very way, with:

1. a cross over a circle where the circle is “the zodiac” and the lines of the cross the solstitial and equinoctial colures; and
2. the direction of progression of the Sun through the zodiac going counterclockwise.

These two correspondences, taken together, must surely indicate that, at least for this usage, The Zodiac was conceptualising his chosen symbol in terms of nothing other than the celestial zodiac. Indeed, with the same evidenced clearly here, we must at least be open to the idea that this is precisely how he had conceptualised the use of this symbol all along.

We get some degree of support for the above claim when we turn to look at how the symbol was again used later as a ‘compass rose’, setting the origin of coordinates for use on the Phillips 66 map.

In this case, then, he again gives us the circle divided by 12 points. Only now, because the usage is one of defining merely a bearing (with no additional astronomical associations) he:

1. chooses the clockwise direction for his numbering; and
2. has the zero at one of the cardinal points.

As he did not, likewise, take this simplistic approach for the previous figure, we can be confident that the choices he made there were deliberate and for a specific reason, as demonstrated.