You are correct, the answer is A) shaft eccentricity. A dial indicator is used to measure the amount of eccentricity or runout in a rotating shaft. This helps determine if the shaft is properly aligned and not wobbling or out of round. Dial indicators are a common tool used to inspect the condition of rotating machinery and ensure proper shaft alignment. The other options are incorrect because: B) Torque of a shaft is typically measured using a torque wrench, not a dial indicator. C) Dial indicators are not commonly used to measure scribed layout lines on vertical surfaces. D) Dial indicators can measure both positive and negative readings to indicate the amount of eccentricity.