Ancient Chinese timekeeping utilized the "Ten Heavenly Stems" ( Tian Gan ). A ten-day cycle formed a basic unit of time known as a Xun (旬). Medical theory posits that the Wei Qi (defensive energy) circulates through the body’s meridians in a complete cycle related to these numerical progressions. Therefore, a ten-day period represents one complete cycle of defensive Qi renewal. The "Watching" aspect implies a period of vigilant observation by the physician to see if the pathogen is expelled or retreats deeper into the organs within one full cycle of Qi.

For natural contraception, the rules are stricter. You must follow the or "Double-Check Rule" :

The project was simple: for 10 days, Fu had to watch a specific spot in the city without moving or interacting with anyone. She chose a small park bench in a bustling downtown area, and on the first day, she sat down and began to observe.

At first, it was awkward. People would glance at her, wondering what she was doing, but Fu just sat still, taking in every detail. She noticed the way the sunlight filtered through the trees, the sound of birds chirping, and the smell of freshly cut grass.