Placing a liquid measuring cup on a flat surface and checking at eye level ensures an accurate measurement by eliminating parallax error, which occurs when the liquid level appears different depending on the viewing angle.
When measuring liquids, accuracy is crucial for consistent results, especially in baking and cooking. Liquid measuring cups are designed with markings on the side to indicate volume. However, the surface of a liquid in a container often forms a meniscus, a curved shape due to surface tension.
If you hold the measuring cup up in the air, it's difficult to ensure it's perfectly level. Even a slight tilt can cause the liquid level to appear higher or lower than it actually is. Similarly, viewing the liquid from an angle introduces parallax error. If you look down at the cup, the liquid level will appear higher than it is. If you look up at the cup, the liquid level will appear lower.
By placing the measuring cup on a flat, level surface, you eliminate the tilt. Then, by bringing your eye level with the surface of the liquid, you ensure that you're reading the measurement at the true point of the meniscus, leading to a more accurate measurement. You should read the measurement at the *bottom* of the meniscus.
Always use a liquid measuring cup for liquids and a dry measuring cup for dry ingredients. Liquid measuring cups have a spout for easy pouring and extra space above the measurement line to prevent spills, while dry measuring cups are designed to be filled to the brim and leveled off.