When is a mercury-tube pressure control most accurate?

A mercury-tube pressure control is most accurate when installed vertically. In a vertical position, the mercury can move freely without obstruction, which allows for more precise measurements of pressure changes. This vertical alignment ensures that the gravitational pull on the mercury column is consistent, providing stable and accurate readings.

When installed horizontally, the fluid dynamics can complicate the readings due to potential stagnation or uneven distribution of the mercury, which may lead to inaccuracies. Additionally, while calibration and connection to a power source are important for the functionality of pressure controls in general, they do not directly enhance the specific measurement capabilities of the mercury tube itself. Therefore, the vertical installation is the factor that allows for the greatest accuracy in pressure measurement with this type of device.