A Solid Balance Beam

I pushed past the garden gate latch and ducked right into the open wooden tool shed for some indoor agility training! Right on the lower shelf of the cluttered workbench lay a heavy yellow spirit level, its glass vial glowing with a bright neon-green bubble. Ha! The ultimate coordination test! I hopped onto the dusty wooden plank, planted both broad feet squarely atop the level's smooth aluminum rail, and balanced my stance. With a hearty chuckle, I leaned my weight slowly from my left heel to my right toes. Tilt left, tilt right—whoosh! The trapped bubble glided straight between the two thin black marker lines and held dead center. Perfect equilibrium achieved!