246 degrees is 4 radians + 17 degrees.
When the Phillips 66 Road Map was mailed on June 26th 1970 Magnetic North was approximated at just under 17 degrees.
4 radians = 4 X 57.296 = 229.184 + 17 degrees = 246 degrees.
So apparently the Zodiac Killer was very familiar with radians and the value of Magnetic North, unless we are assuming he was just lucky in his placement of the bold circle on the diagram. His further reference to SFPD next to this circle, makes one think this is where we should be centering our focus.
The final confirmed murder of the Zodiac Killer was that of Paul Stine at Presidio Heights on October 11th 1969 and in his letter mailed one month later on November 9th he again ridicules the police and lays out the details for his construction of a bomb.
Paul Stine had picked up his final paying fare that night from Pier 64 to the Air Terminal at San Francisco International Airport, before returning back to the theater district near the Mason and Geary intersection. This is where it is believed he picked up the Zodiac Killer for one last fateful journey.
We know the Zodiac Killer mentioned radians and inches along the radians, so let us start with complete radians. We know from above that the value of 4 radians is significant, so this being 229 degrees, we shall place a compass rose over Mount Diablo and see where this takes us, in respect of San Francisco.
Was the Zodiac Killer intending to ratchet up the fear by exploding bombs in the vicinity of the airport. Of course this hypothesis is just pure speculation, or is it. Let us take a further look at the Button Letter mailed on June 26th 1970, where the Zodiac Killer stated 'The Map coupled with this code will tell you where the bomb is set. You have until next Fall to dig it up,' and enter something alongside the code.
SEE PART TWO - http://www.zodiacciphers.com/zodiac-news/sfi-airport-part-two-hunters-point