"Mr. Albright offers a quick lesson in nuclear science: For uranium to be weapon-grade, it must be enriched to 90%. “Enrichment is a complicated process,” he explains. “If you start with natural uranium and enrich it to 5%, where you’re not even close to 90%, that’s actually 70% of the enrichment effort.” The math, on its face, is misleading. “When you’re at 60%, it may look like you’re 30% short on percentage, but you’re actually 99% of the way in terms of enrichment effort.” In other words, 60% enrichment is only a hair’s breadth from weapon grade—and Iran’s program is brimful with this near-weapon-grade uranium."
WSJ: Iran Is Down, but Not Yet Out