The Zodiac Killer realized that the information he provided in the Button letter was insufficient to discover where he was planning to set the bomb. He also realized it was insufficient to solve the 32-Symbol cipher. That is why he placed two crosshairs in his next communication on July 26th 1970. One of the crosshairs contained the radians value, while the other crosshairs contained the inches value. Zodiac wrote:
"P.S. The Mt. Diablo code concerns Radians + # inches along the radians".
The second crosshairs had the phrase "P.S. The Mt. Diablo code concerns Radians + # inches along the radians" written over it. Why would the Zodiac Killer place an arrow pointing before the inches value, if he didn't intend for us to place a number here? The answer could only ever be 5 inches, because using the Phillips 66 map scale of 6.4 miles to the inch, only 5 inches falls over San Francisco (4 & 6 falls into the sea).
The target of SFPD was therefore 4 radians and five inches from Mount Diablo. The target was the Southern Freeway by Ingleside Police Station, explained in greater detail here.
Whatever target the Zodiac Killer chose, it was extremely unlikely his radians and inches values would form whole numbers. This is why he gave us an estimate. On December 3rd 2020, David Oranchak, Sam Blake and Jarl Van Eycke solved the infamous 340 cipher after 51 years. On December 27th 2020, just twenty-four days later, Druzer (a regular contributor to both mainstream Zodiac forums) solved the 32-Symbol cipher. When four radians and five inches was placed into the 32-Symbol code with the word estimate, it married perfectly the three repeating ciphertext characters, giving us the complete solution to the code. The simplicity of this solution is its strength, because it doesn't require an explanation longer than the idea. I have zero doubt his solution is correct, which is why I am satisfied that the search for answers to the 32-Symbol cipher is over.