Sera had a system.

Every morning she woke before the first guard change, which happened at what she had calculated was roughly dawn based on the way the air in the corridor shifted when the outer doors opened. She ate whatever they brought without complaint because complaining gave them something to respond to and she didn't want to give them anything. She watched the guards during the meal and updated her count.

Fourteen guards total on their level. Six on rotation at any given time. The rotation changed every four hours except the one at midnight which ran six hours because the guard they assigned to midnight was the one...