(CNN) The devil is in the details.
That adage is particularly true for a deal as contentious and complicated as the one reached Tuesday over Iran's nuclear program.
Iran and its longtime adversaries, including the United States, have been working at it for years. In a relationship long rife with mistrust, checks and counterchecks are a must for any agreement. It's a logistical challenge to figure out how to inspect sensitive, highly secured sites around a large country. And this is nuclear science we're talking about, after all, hardly a topic to breeze through casually.
Here are some highlights from the historic agreement announced in Vienna, Austria, as related by the U.S. government and Iranian state media.
Deal aims to limit nuclear threat, open trade
Does this deal eliminate Iran's nuclear program? Or does it let it continue unimpeded?
No and no. The truth lies somewhere in the middle.
The Joint Comprehensive Plan of Action, as this deal is being called, states point blank that "Iran reaffirms that under no circumstances will (it) ever seek, develop or acquire nuclear weapons." The distinction is between nuclear weaponry and nuclear power.
Iran's state-run Islamic Republic News Agency stresses that, under the deal, "world powers have recognized Iran's peaceful nuclear program and are to respect the nuclear rights of (Iran) within international conventions." By this, it means a country's right -- including Iran's, since it signed the Treaty on the Non-Proliferation of Nuclear Weapons -- to enrich nuclear fuel for civilian purposes.
The IRNA report stresses no Iranian nuclear facilities or centrifuges will be dismantled, including the Arak heavy water reactor. It also states "the policy of preventing enrichment uranium is now failed and Iran will go ahead with its enrichment program." And Iranian students now can be allowed to study in nuclear fields.
But none of this means Iran's nuclear program won't change significantly.
Iran's government didn't focus on what its government must do to diminish its nuclear program, but the U.S. State Department did, in its synopsis of the agreement. It says that Iran will:
• Keep its uranium enrichment levels at no more than 3.67%, down from near 20%.
• Maintain a uranium stockpile (at the above prescribed level) under 300 kilograms, well below its current 10,000-kilogram stockpile. President Barack Obama says this works out to Iran reducing its nuclear stockpile by 98%.
• Phase out its IR-1 centrifuges within 10 years, keeping over 5,000 centrifuges running during this stretch at its Natanz facility. "Excess centrifuges and enrichment-related infrastructure at Natanz will be stored under IAEA continuous monitoring." (The IAEA is the International Atomic Energey Agency, the U.N.'s nuclear watchdog.) Nationwide, Obama said that Iran will put away about two-thirds of its roughly 19,000 current centrifuges.
• Not have any nuclear material at its Fordow facility for 15 years, converting that site "into a nuclear, physics and technology center."
• Limit certain research and development activities for the next eight years.
• "Design and rebuild a modernized heavy water research reactor in Arak ... using fuel enrichment up to 3.67%" after getting international authorities' OK on the final design. "The reactor will support peaceful nuclear research and radioisotope production for medical and instructional purposes." Iran will not add any other heavy water reactors for the next 15 years.
• Ship spent fuel outside its borders.
Of course, it's not as simple as Iran signing a piece of paper, agreeing to a bunch of things, and this yearslong impasse being over. For the United States, European Union and others to believe Iran is living up to the bargain, they have to see it -- through the eyes of inspectors.
"This deal is not built on trust; it is built on verification," Obama said. "Inspectors will have 24/7 access to Iran's key nuclear facilities."
The IAEA will take the lead. That group and Iran have already signed a "road map" outlining a process that IAEA Director General Yukiya Amano said aims "to make an assessment of issues relating to possible military dimensions to Iran's nuclear program by the end of 2015."
"It sets out a clear sequence of activities over the coming months, including the provision by Iran of explanations regarding outstanding issues," Amano added. "It provides for technical expert meetings, technical measures and discussions."
Inspectors look likely to spend the bulk of their time at Iran's established nuclear facilities like Natanz, Fordow and Arak. They'll have a number of tasks:
• Monitor uranium levels "from all uranium ore concentration plants for 25 years," according to the State Department.
• Keep an eye on all centrifuges (including those Iran will store, per the agreement) for 20 years to ensure Tehran is abiding by the agreement.
• Communicate back and forth with Iranian officials over the next few months to get explanations on key points and address "any possible ambiguities."
• Maintain a "long-term presence in Iran," beyond its specific objectives.
Iran doesn't have to grant permission for inspectors to go somewhere, said White House deputy national security adviser Ben Rhodes, because Washington and its European allies have enough votes to make it so.
"If they don't grant access," Rhodes said, "they violate the deal."
The big worry of U.S. and allied leaders wasn't that Iran might have nuclear energy, but that it would have nuclear missiles and bombs.
Thus, Iran's military -- which would have a role in weaponizing such technology -- has to be part of the discussion.
The IAEA chief noted his agency and Iran have reached "a separate agreement regarding the issue of Parchin," a military site. This suggests international inspectors will get some access at least to that base southeast of Tehran, though it's not clear how much or if they'll be able to check on other military sites.
Because of the deal, Iran said it soon will no longer face the restrictions that have long affected its military. There will still be limits on ballistic missiles, IRNA pointed out, but only on "missiles designed for nuclear weapons."
The same state news report added that "Iran's arms embargo (will) be lifted or be replaced with some restrictions," some of which might be addressed on a case-by-case basis. "These restrictions will be completely removed after five years."
It's not clear to what extent all parties to the Vienna agreement, though, will loosen up on military matters. The United States, for instance, insists that it will continue to enforce sanctions tied to "Iran's support for terrorism, human rights abuses and missile activities."
To what extent, though, remains to be seen.
Why did Iran make this deal? Yes, leaders in Tehran have claimed they never wanted nuclear weapons in the first place. But their main reason to act now is to lift various international sanctions that have hurt Iran's economy for years.
President Hassan Rouhani has stressed since his 2013 election campaign that one of his priorities is to help his country financially by making it less isolated and more a part of, rather than a target of, the international community. Having a nuclear deal is pivotal to that plan, with IRNA saying it paves the way for "broadening ... cooperation with other countries."
No surprise, then, that Iranian state news reported prominently that "all unfair sanctions imposed by the U.N. Security Council ... are to be lifted" and similar punishments levied by the European Union and U.S. governments should be phased out as well.
These moves should include ending a ban on Iran's purchase of passenger airplanes, dropping sanctions on the country's central bank and oil company, and unfreezing "tens of billions of dollars of Iran's revenues," according to the Iranian state news report.
The United Nations' moves should come once "the IAEA-verified implementation of agreed nuclear-related matters by Iran" is complete, the State Department said. While the U.S. government will keep other sanctions, it has agreed to drop those tied to Tehran's nuclear program.
There's a catch, though. Obama will submit the deal to Congress to review for 60 days, opening the door for legislators to nullify the pact. The President doesn't seem inclined to budge, however.
Obama faces hard sell to Congress
"I will veto any legislation that prevents the successful implementation of this deal," Obama said.
Yet the U.S. President also emphasized that he is ready to abandon the agreement if Iran doesn't abide by it.
"If Iran violates the deal, all of these sanctions will snap back into place," he said. "So there is a very clear incentive for Iran to follow through and there are very real consequences for a violation."