When it comes to the state of the Iran nuclear deal, there are enough figures flying around to make your head spin like atoms in a first-generation gas centrifuge.
Uranium-235; 3.67-percent enrichment; a 300-kilogram cap; Paragraph 36 of UN Resolution 2231 -- it has become a dangerous numbers game as Iran and the United States play chicken over Iran's nuclear program.
Here's a little guide to help you keep track of the score:
On July 1, the International Atomic Energy Agency (IAEA) verified that Iran's stockpile of low-enriched uranium (LEU) had exceeded 300 kilograms, breaching the limit set in a 2015 nuclear deal worked out between world powers and Iran.
The development placed the future of the already troubled deal -- which intended to provide assurances that Iran could not develop a nuclear weapon and had reduced Tehran's stockpile of LEU by 98 percent -- under heightened scrutiny.
Daryl Kimball, executive director of the nonpartisan Washington-based Arms Control Association, noted that Iran had a stockpile of 11,500 kilograms of low-enriched uranium prior to the signing of the deal in July 2015.
"It takes roughly 1,050 kilograms of LEU in gas form and enriched to weapons-grade (90 percent) to produce a significant quantity (25 kilograms) for one bomb," he wrote in comments to RFE/RL.
A week later, Iran announced that in keeping with a warning issued two months ago it had begun enriching uranium above the 3.67-percent concentration level set in the nuclear deal.
This claim, confirmed by the IAEA on July 8, was met with alarm by former and current parties to the nuclear accord, known formally as the Joint Comprehensive Plan Of Action (JCPOA).
The European Union said it was "extremely concerned" by the latest development, while U.S. President Donald Trump warned that "Iran better be careful."
"Both edging past the 300-kilogram limit and edging up beyond 3.67 percent would reduce the time required for Iran to produce a bomb's worth of material," according to Matthew Bunn of Harvard University's Belfer Center for Science and International Affairs.
But the nuclear-policy expert and Harvard professor noted in written comments to RFE/RL that the measures would cut down Iran's so-called breakout time "only by a little -- and both are completely reversible."
"They are putting pressure on the Europeans and the others to deliver on the promises of sanctions relief contained in the deal, but in ways that would allow them to return to the deal easily if they get what they want," Bunn said.
The latest controversy can be tied to disagreements over compliance, or lack thereof, with the commitments outlined in the JCPOA, which was endorsed by the UN Security Council through the adoption of Resolution 2231 in July 2015.
The resolution freed the world governing body to verify and monitor Iran's nuclear-related commitments under the JCPOA and was considered by the Security Council as a "fundamental shift in its consideration of the Iranian nuclear issue."
Worked out between world powers and Tehran over two years of negotiations, the 2015 nuclear deal provided assurances that Iran would be prevented from potentially producing a nuclear weapon by placing physical limitations on the country's ability to produce fissile material.
In exchange, Tehran -- which has denied seeking to produce nuclear weapons -- received relief from economic sanctions imposed by the United States, the EU, and the United Nations that were severely hampering Iran's economy.
Much of the deal centered on curtailing Iran's ability to enrich uranium-235, which can be split to release energy and, depending on its concentration, can be used to fuel nuclear reactors or potentially weapons. Once uranium-235 is isolated using a cascade of centrifuges, it can be increasingly enriched.
Richard Nephew, an expert with the Washington-based Center for Arms Control and Non-Proliferation, told RFE/RL that setting a cap of 3.67 enrichment under the deal "was less significant than the idea of the lower the level of enrichment the better."
"This amount is what is typically used for power reactor fuel," said Nephew, an adjunct professor and senior research scholar at Columbia University's School of International and Public Affairs. "So it was a convenient figure."
The deal was signed by the five permanent members of the UN Security Council -- the United States, China, France, Russia, and Britain -- plus Germany, as well as by Iran and the EU.
President Trump, asserting that Iran was violating the spirit of the deal and continuing to pursue nuclear weapons, withdrew the United States from the JCPOA in May 2018.
In addition to reimposing U.S. sanctions that were lifted or waived under the agreement, the United States introduced new, secondary, sanctions on countries that did business with Iran.
10 To 15 Years
The JCPOA contained so-called sunset clauses that over time were to lift the physical restrictions placed on Iran's nuclear activities.
Harvard's Belfer Center, which has maintained a definitive guide to the deal, wrote that the "JCPOA buys at least 10 to 15 years before Tehran can significantly expand its nuclear capabilities."
But Trump listed the sunset clauses, whose expiration could allow Iran to build up its nuclear infrastructure, among the "deal's many serious flaws" when he first declined to certify Iran's compliance with the deal in October 2017.
After the U.S. withdrawal, it was left to the EU3 -- Britain, France, and Germany -- to try to maintain the deal along with fellow signatories China, Russia, and Iran.
"European powers, plus China and Russia are seeking to preserve the deal by sidestepping the U.S. secondary sanctions," allowing for legitimate trade with Iran, according to Kimball.
"They are also urging Iran to exercise restraint and stay within the limits of the JCPOA," he wrote. "They hope these and other measures will lead Iran to reconsider its plan to continue to exceed certain JCPOA nuclear limits.
4.5 Percent And Over
After giving notification that it had breached the 3.67 percent limit, Iran clarified that it had exceeded 4.5 percent enrichment.
The Arms Control Association's Kimball wrote on July 8 that "this is another violation," but "does not pose a near-term proliferation threat."
"What would be worrisome is if Iran began to enrich to 20 percent or higher and began to accumulate a larger and larger stockpile," he wrote.
However, he added: "It is our assessment that Iran's latest steps to breach certain nuclear limits agreed to in 2015 are not an attempt to race to acquire nuclear weapons, but rather it is an attempt to create the political leverage to press the remaining parties to the 2015 Iran nuclear deal to redouble efforts to deliver on the economic relief from sanctions that Iran was promised under the deal."
Iran has said that it has abided by the nuclear deal and has followed the dispute-resolution mechanism laid out under Paragraph 36 of the JCPOA.
It reads, in part, that if after a series of steps "the issue still has not been resolved to the satisfaction of the complaining participant, and if the complaining participant deems the issue to constitute significant nonperformance, then that participant could treat the unresolved issue as grounds to cease performing its commitments under the JCPOA in whole or in part."
Foreign Minister Mohammad Javad Zarif, in a July 7 tweet announcing that Iran was increasing its level of uranium enrichment, repeated Tehran's allegation that the signatories to the deal had failed to take action to relieve the renewed and new sanctions imposed by the United States.
Abbas Araqchi, Iran's deputy foreign minister, vowed on July 8 to take a third step within 60 days "if remaining countries, especially Europeans do not act seriously on their commitments" and provide relief from U.S. sanctions.
While he did not specify what the move would be, Araqhchi said it would be "stronger."
This was widely seen as a threat to restart centrifuges mothballed under the nuclear deal and to increase uranium enrichment to 20 percent purity, Iran's highest level of uranium enrichment achieved before the 2015 accord.
"Just under 20 percent (about 19.75 percent) is the level of enrichment needed for fuel for the Tehran Research Reactor," Bunn wrote. "It would also mean they had done about 90 percent of the work of producing nuclear bomb material, giving them an even better head start should they decide to leave the agreement."
Prior to the 2015 deal, the United States had estimated that Iran had reached the capability to develop a nuclear weapon within two to three months. A big part of the accord was to increase that period to one year.
As for how much Iran might have reduced its breakout time with its latest measures, Nephew of the Center for Arms Control and Non-Proliferation said, "It will be iterative."
"This specific step has not reduced breakout time at all really," according to Nephew. "But, the more enriched uranium they get, the closer the breakout timeline becomes. At 1,200 kilograms of 3.67 percent with 5,000 centrifuges, they're about five-to-six months away, perhaps less."