(In reply to
Tracking this by Charlie)
A web search shows that the frequencies for the rows and columns are as shown at the left and bottom of this chart:
697 1 2 3
770 4 5 6
852 7 8 9
941 * 0 #
1209 1336 1477
While the difference between 852 and 770 is the same 82 as the difference between 2188 and 2106, the difference between 770 and 697 is 73not the 163 difference between 2106 and 1943.
If we were to encode by adding the row Hertz value to the column Hertz value, we'd get:
1 1906
2 2033
3 2174
4 1979
5 2106
6 2247
7 2061
8 2188
9 2329
The numbers for 4 through 9 match those used in the puzzle. It looks like the puzzle's codes for 1 through 3 erroneously used 607 instead of 697 as the top row frequency in Hertz.
Once this is corrected, we can assume the bottom row frequency is 941. Added to the 1336 for the middle column, this gives 2277 as the representation of zero, and therefore the next 4digit number in the sequence.
Of course on the actual telephone the combination of frequencies is not by adding the Hertz, but by combining the tones, which then would actually beat at the difference between the Hertz values.

Posted by Charlie
on 20050406 13:45:45 