North Korea's latest nuclear weapons test is much more powerful than the previous two, according to estimates made by instruments that measure seismic waves from the blast. It's about the size of the bomb that devastated Hiroshima in World War II.
But it's not so easy to verify the claim that the nuclear explosive has also been miniaturized. That's a critical claim, because a small warhead would be essential if the rogue regime chose to threaten the United States with a nuclear-tipped missile.
Big bombs are easier to make, but they aren't all that useful as a threat.
"It doesn't do the North Koreans much good if they have to put it in a truck," says Jeffrey Lewis, the director of the East Asia Non-Proliferation Program at the Monterey Institute of International Studies. But the threat level obviously rises as the bombs get more compact.
And that's the claim with the North Korean nuclear test.
"KCNA, the Korean news agency, has come out and said it was a smaller and light design, I believe were the exact words," says James Acton, a senior associate in the nuclear policy program at the Carnegie Endowment for International Peace.
There's a related issue in the question of North Korea's ballistic missile capability. Despite their much-ballyhooed - and failed - 'satellite' launches, North Korean engineers probably aren't up to the task of building a re-entry vehicle for an intercontinental ballistic missile. They may, however, be able to produce a shorter-range missile and warhead combination in the near future that could menace US allies in the region.