A True Level

The painted sill gave clear vision, but the high study shelf demanded night surveillance. Leaping across from the window frame, I secured a foothold atop a heavy row of hardcovers. Resting flat on the dark wood was a small yellow spirit level. Its neon-green vial glowed faintly under the desk lamp below, but the tiny black air bubble floated off-center, nudged askew by a leaning steel bookmark. I planted my boots firmly on the shelf edge, gripped the rectangular plastic casing with both hands, and applied steady lateral force. The bubble drifted smoothly through the viscous fluid until it locked precisely between the two printed black guide lines. Absolute horizontal balance. Position secure for the night.