Open, the site's label. The site's commentary calls this the sparse ruler problem: Rédei asked whether the limit exists, Erdős and Gál proved that it does (claim page (Erdős and Gál, 1948), which also records a slip in the paper's printed covering argument and the parts of its theorem that are not covered), and the limit lies in $[1.56,\sqrt3]$, the lower bound Leech's (claim page (Leech, 1956)) and the upper bound Wichmann's (claim page (Wichmann, 1963)); each is recorded as an accepted partial claim on its refereed publication, none on acceptance by the site, whose label leaves the problem open. Pegg's computations, which the commentary cites as evidence that $\sqrt3$ is the value, prove nothing about the limit and have no claim page. Bernshteyn and Tait (J. Number Theory 205 (2019)) showed that Leech's constant is not sharp, without a new numerical bound; that is recorded on Leech's page. The value of the limit is open. The commentary also raises the variant without the restriction $A\subseteq\{0,1,\ldots,N\}$, the unrestricted difference bases of Rédei and Rényi, which is not the problem's question.