What is a characteristic of mercury column measurements?

Mercury column measurements are particularly known for their ability to measure vacuum levels. A mercury barometer, for instance, utilizes a column of mercury to display atmospheric pressure, and when measuring vacuum, it indicates how much less than atmospheric pressure is present. This can be useful in various applications where maintaining a vacuum is crucial, such as in laboratories or in certain industrial processes.

The other options do not accurately describe the characteristics of mercury column measurements. Measuring only above zero is incorrect because mercury columns can measure both positive pressure and vacuum levels (negative pressure). While calibration might be necessary for specific applications to ensure accurate readings, it is not a fundamental characteristic of mercury column measurements themselves. Lastly, mercury columns are not restricted to measuring high pressure; they can accommodate a range of pressures, including low and vacuum pressures.