How long had David been on Plant 4 when the Covenant crew arrived?
Hydrated, nourished, interested, Rosenthal discovered that against all odds, she was bored. Wondering over to one wall of the downed chamber, she found herself running her fingers over a long row of hashmarks that have been carved into the otherwise immaculate stone.
Each was exactly the same height, width, and depth as the one next to it – all three thousand, eight hundred, and some odd. No human could be so precise, and there was nothing about them to think that they had been made by the Engineers. The marks had to have been inscribed by David.
Alien: Covenant novelization page 219
The line of precise hashmarks inscribed in the corridor seemed endless. Her fingertips dancing along the wall, Rosenthal‘s hand rose and fell, rose and fell, as she traced the marks, letting them lead her onward. Lost in her own exploratory revere, it did not occur to her that she had left the domed chamber a considerable distance behind.