Instrument Used to Measure Egg Shell Strength

Correct Answer: Screw gauge

Shell strength (and shell thickness) are measured using a Screw gauge. Shell strength is directly proportional to shell thickness.

Vernier Caliper vs. Screw Gauge

• Vernier caliper: Measures external dimensions with accuracy of 0.1 mm → used for ESI (egg length and width).
• Screw gauge (micrometer screw gauge): Measures much smaller distances with accuracy of 0.01 mm → used for shell thickness (0.30–0.50 mm).

ESI Formula

ESI = (Maximum width / Maximum length) × 100

• ESI of chicken egg: 74
• ESI of duck egg: 72
• ESI of quail egg: 78
• High ESI = more rounded egg; Low ESI = more elongated egg.

Why Other Options Are Wrong

• Vernier caliper → used for ESI, not shell strength.
• Brine flotation → used for specific gravity, not shell strength.
• Micrometer → although similar to screw gauge, the standard term used is 'Screw gauge' in poultry science.