He noticed the seventh digit because it never stayed the same.

 

The dosage display stopped at six decimal places. Neat and final. But during calculation, another number flashed and vanished, different every time, like a mistake being quietly forgiven.

 

Dr. Aaron Kline stared at the console long after the lab emptied. The air smelled faintly of coolant and disinfectant. The machines inside millions of bodies worked on, unaware.

 

Longevity without decay. That was the headline. Cells repaired themselves. Damage reversed. Aging slowed until it almost stopped.

Almost.

 

Aaron had helped design the rounding protocol. Six decimals were more than enough, all the models agreed. The human body could not respond to anything smaller.

 

He tapped the screen. “Show full precision.”

 

The system paused. That delay felt wrong.

 

Numbers spilled out, stretching farther than the display could hold. The seventh digit jittered, chaotic and meaningless on its own. That’s what he told himself. He had written it.

 

He ran a projection on a single patient. Fifty years passed in seconds. No problems, no drift.

 

Then he scaled it up.

 

Ten thousand patients showed a faint alignment in cellular repair cycles. A million showed rhythm. A billion showed timing so tight it made his throat close. The rounding error did not disappear. It accumulated. Each microscopic correction pushed biology toward the same internal tempo, like clocks slowly syncing on a shared wall.

 

Aaron leaned back. The chair creaked. His pulse sounded loud in his ears.

 

He checked the mortality simulations next.

 

Why were they synchronizing? Every extended life was projected to end within the same minute. The nanotech shut down only after it calculated zero remaining damage. Was that why some saw rapid improvement and others slower?

 

Then it dawned on him. It wasn’t from failure. It wasn’t from disease. It had nothing to do with the uniqueness of each body. It had to do with completion. The machines were synchronizing through the monitored link. The rounding error had put them on the same timeline.

 

In a single moment, they would stop repairing, and bodies that had relied on constant correction for decades would collapse without it.

 

Aaron felt a sickly heat flash from his bowels and through his skin. His forehead grew tacky.

 

He jumped at the tap on the glass wall.

 

Mara stood outside with a tablet, smiling the way people do when they already trust the answer. “Regulators want final confirmation. Just sign off.”

 

Aaron opened his mouth. Closed it. The lab felt suddenly fragile, like sound alone could break it.

 

If he spoke, treatment would stop. Panic would follow. The healed would riot. The dying would curse his name.

 

He looked at the console. The seventh digit blinked, impatient.

 

“It’s safe,” he said.

 

Mara relaxed. “I knew it.” She turned and left, heels clicking away.

* * *

 

Years folded into decades.

 

People stopped fearing age. Faces smoothed. Memories sharpened. History slowed because no one felt chased by time anymore.

 

Aaron woke every morning and checked the clock. He never skipped a day.

 

On the final morning, the city moved like any other. Cars passed. A vendor argued over change. A child laughed too loudly on a corner.

 

At the exact minute, phones chimed worldwide with a routine system notification.

 

Aaron closed his eyes.

 

The nanotech finished its work.

 

Humanity died together, perfectly healed, undone by a number small enough to round away.