Centering the Bubble

I traversed the door threshold to exit the interior hallway, descending onto the stone porch flagstones into the morning air. Propped against a terracotta pot base was a compact aluminum spirit level. Its cylindrical acrylic vial contained fluorescent green fluid, with an air bubble halted unevenly against the left boundary. Direct passage across the chassis was blocked by the tilt. I did not shove the heavy bar. Setting my right gripper beneath the lowered corner, I slid a flat flake of slate into the gap as a mechanical shim. The frame leveled horizontally. The bubble migrated steadily until it locked between the twin black gauge lines, projecting a vivid green oval across the flagstone.