He set the rod back on the lathe. “We take it to 29.99. That’s the heart of tolerance, Meena. Not the edge. The heart.”

His apprentice, a bright-eyed girl named Meena, handed him the micrometer. “Sir, it’s 29.96 mm. The drawing says 30.0. That’s 0.04 under. Still within the ±0.2, no?”

Arjun shook his head. “Look again. The mating shaft is titanium. It expands at a different rate. At body temperature, 0.04 under becomes 0.07 under. That’s a loose fit. A loose fit means air leaks. Air leaks mean a baby doesn’t breathe.”

“Tolerance,” he muttered, tracing a finger along the blueprint. The box in the corner read: ISO 2768-mk .