How will Iran's nuclear deal be policed?
If Iran keeps or breaches promises it made when it signed a deal over its nuclear programme, it will be up to one group to confirm the news to the world.
The International Atomic Energy Agency, the IAEA, has been given a crucial role in the new agreement with Iran.
The Vienna-based nuclear watchdog will be the "eyes and ears of the international community" in Iran, according to its Director General, Yukiya Amano.
It is challenging, complicated and diplomatically delicate work.
The agency's inspectors have to verify whether Iran is living up to its side of the bargain.
It must cut back its nuclear infrastructure and drastically reduce its stockpile of low enriched uranium, in return for sanctions relief.
Under the deal, Iran has also agreed to implement the IAEA's Additional Protocol, which gives the inspectors much more access.
Laura Rockwood, former Senior Legal Advisor to the IAEA's Department of Safeguards, says this move will give inspectors "a more complete picture" of Iran's nuclear programme.
"It's a bit like a jigsaw puzzle," she says. "The more pieces the IAEA has of the puzzle that is Iran's nuclear programme, the easier it is for the agency to see whether the puzzle fits the picture of a peaceful nuclear programme."
The IAEA already has inspectors on the ground in Iran, but diplomats say all this will significantly increase their workload, as well as put pressure on the agency's budget.
Robert Kelley, a former IAEA director of inspections, says the specialised nature of the work means the agency cannot hire very quickly.
"Increased effort [in Iran] will result in decreased effort in other countries," he said.
However, he says more advanced technology is certainly a help for the inspectors.
"A simple case is the move from film to digital cameras, both hand-held and in the facilities," he says.
Other new tools include fibre-optic smart seals, which can send out alerts if they are tampered with.
Mr Kelley says their use will reduce the constant need to bring old-fashioned hand-tied metal seals to Vienna for verification.
"There are also new tools like an online enrichment monitor that will tell the inspectors what [levels of] enrichment is in a pipe or drum without having to take physical samples and bring them to Vienna for analysis," he says.
More cutting-edge technology is available at the IAEA's recently-upgraded laboratories in Seibersdorf, near Vienna.
Upgrades include a new €3.8m ($4.2m, £2.7m) mass spectrometer, which can detect minute traces of nuclear material.
Make or break
The strains on the IAEA are not just financial, however.
Iran has also agreed to address the agency's long-running concerns about possible military dimensions (PMD) to its nuclear programme by mid-October.
Both supporters and detractors of the deal will be watching closely to see whether Mr Amano declares that Iran has co-operated or not.
Some diplomats fear Iran will drag its feet as it has done in the past. Others say it now has strong motivation to respond to the agency.
Mr Amano will then file his assessment to the IAEA's board of governors by December. That report is likely to come under intense scrutiny.
In the past, Iran has accused the agency of bias. Others fear there could be a whitewash to save the deal.
In a recent BBC interview, Mr Amano stressed the technical nature of the IAEA's work and the need for Iran to be "as transparent as possible". But the nuances in his report could, in theory, make or break the deal.
Tariq Rauf, a former senior IAEA official who is now at the Stockholm International Peace Research Institute, says no-one is expecting a confession from Iran.
"This essentially will be a compromise solution to an otherwise insoluble problem created by the intelligence information supplied by Israel and the US to the IAEA that cannot be independently and credibly verified by the agency," he says.
He says the IAEA's assessment, which he describes as an "elegant and practical way to move forward" is "designed to close the issue by 15 December 2015".
If the IAEA is able to report that Tehran has kept its promises - both on scaling back its nuclear work and answering questions on the PMD - it will trigger relief of the sanctions which Iran has sought an end to for so long.