Final answer:
The specific gravity of distilled water used to calibrate a refractometer should be 1.000, as specific gravity is a ratio that compares the weight of a liquid to that of pure water.
Step-by-step explanation:
When distilled water is used to calibrate a refractometer, the specific gravity should be 1.000. This is because specific gravity is a measure of the weight of a liquid compared to pure water, and pure water itself has a specific gravity of 1.0 at room temperature.
The presence of any solute in water increases its specific gravity, so distilled water, which is pure, naturally has a specific gravity equal to the baseline value of 1.0.