Scientists utilize measuring equipment that is calibrated for accuracy. This minimizes the margin of error and therefore enables accurate comparisons of matter. The ability to accurately evaluate the qualities of matter through measurement is the basis by which meaningful inferences can be made.

A graduated cylinder is a tube calibrated with even increments of measurement. A common unit of measure for liquids is the Liter. A small graduated cylinder may hold 100 mL, or one hundred milliliters. The length of the cylinder is demarcated with tick marks in increments of 10 mL, with smaller tick marks in between. This can be compared to a ruler. When a liquid is poured into the graduated cylinder, you will observe that the top forms a parabola. This is called a meniscus.

When measuring the volume of a liquid using a graduated cylinder, it is important to read the bottom of the meniscus rather than the top. The distribution of liquid at the top of the meniscus is thin, and contains air from the atmosphere that fills the hollow of the parabola. A calculation of the density of a liquid including this portion would be inaccurate because it includes a portion of gas, which is less dense than liquid. A density calculated by dividing the amount of liquid measured from the top of a meniscus by its mass would therefore be less than the density calculated using the measurement of liquid from the bottom of the meniscus.

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