Dual Tone

Go to the Stephan Leonoudakis Golden Gate Ferry Terminal behind the San Francisco Ferry Building. There you will find two pay telephones.

Some telephone keypads send their signal via Dual-tone multi-frequency. Each row of buttons on the keypad has a sound frequency associated with it; so does each column. When the user presses a key, the keypad combines the sound frequency of the row with that of the column to generate a sound wave.

Combining sound waves is hard. What if we just added frequency numbers instead?

Suppose these payphones' telephone numbers had "frequencies"

24 29 7 21 15 21 21 and

24 29 7 21 9 15 7

...then what would these frequencies mean:

21 24 6 9 24 12 14

_ _ _ _ _ _ _

When you've figured this out, it will tell you to find something else around here.

Back

(Not a clue, just a suggestion: If you're tired and hungry, there are food and drinks in the Ferry Building. If you can't find a place to sit in the Ferry Building, you might wander over to the Stephan Leonoudakis Golden Gate Ferry Terminal and see if there's an empty bench upstairs.)