The man in the cell had worked out a system. He scraped tiny boxes into the cement walls with a piece of stiff wire. The boxes began in the upper left corner above his cot. Since the light that made its way below the iron door was so dim, the man had to squint, his face mere inches from the wall, to see his work.

In each tiny box he etched precise vertical marks. Everytime he heard the faint, single clang of a bell—from what he assumed was the courtyard—he added another mark. The day was over when he had filled the tiny box with 24 scratches. With his piece of wire, he scraped another box beside the completed box, beginning another day. Every seven boxes were enclosed in a larger, rectangular box to mark a completed week.

He couldn’t track the minutes. His piece of wire was too dull to make such hair-thin marks. Plus, the bell in what he figured was the courtyard rang only once per hour, he was pretty sure. There was no accurate way to track the minutes, other than to count the seconds, which entailed a level of concentration he couldn’t muster. The man nodded off now and then, and also he was interrupted by the daily plate of food stuff that slid in beneath the door.

Still, his system—which had already filled two of his cell’s walls with rectangles enclosing tiny boxes containing tinier vertical scratches—was quite effective. If there was anyone to tell, he could explain with mathematical certainty that 89 weeks, 3 days and 17 hours had gone by since he’d found that piece of wire.