Upon final filling of the air meter with water, which part of the liquid level should be adjusted to the zero mark on the meter?

In the context of using an air meter for determining air content in concrete, it's important to understand the behavior of liquids and how they form a curve at the surface, known as the meniscus. The meniscus is the curve seen at the surface of a liquid, which is caused by surface tension.

When finalizing the fill of the air meter with water, the correct approach is to adjust the bottom of the meniscus to the zero mark on the meter. This practice is important for accuracy in measurement. The bottom of the meniscus is the point that is consistently read and referenced in liquid measurements, ensuring that the correct volume is measured.

Other parts of the liquid level, such as the top of the foam or mid-level of the liquid, do not provide an accurate reference for measuring the water level. Adjusting just below the rim would also lead to inaccurate measurements since it may not account for the surface tension of the liquid. Therefore, setting the bottom of the meniscus to the zero mark ensures a standard method for obtaining precise readings.