A Golomb ruler is a set of $n$ integers that determines $\binom{n}{2}$ distinct differences.
Two sets are *homometric* if they determine the same (multiset) of differences.
For example,
$$\{0,1,4,10,12,17\} \;,\; \{0,1,8,11,13,17\}$$
are a homometric pair of Golomb rulers, determining 15 distinct differences (excluding only
$\{14,15\}$).
Although there are arbitrarily large Golomb rulers, and arbitrarily large pairs of homometric
sets (allowing multipiclity), it is unclear (from my searching) if there are arbitrarily large pairs of Golomb rulers.

In the 1994 paper, "There Are No New Homometric Golomb Ruler Pairs with 12 Marks or Less," the authors say that they "are divided on whether any additional nontrivial homometric rulers are to be found." The nice paper "Reconstructing sets from interpoint distances" does not seem to attend to the special case where all distances are distinct. Nor does the Rosenblatt-Seymour paper "The structure of homometric sets" (inferring from secondary sources—I don't have that paper yet).

My question is: What is the largest pair of homometric Golomb rulers known? Is it still open whether or not there are arbitrarily large pairs? Thanks for any pointers on this topic!

**Addendum.** Thanks to Yota Otachi for uncovering the 2007 paper by Bekir and Golomb he cites below.
As he says, it proves that there are no homometric Golomb rulers of more than six marks.
The proof uses Golumb's "polynomial model."

optimal! I'll leave in my incorrect comment above for the record... – Joseph O'Rourke Jul 13 '10 at 20:16