When you visit the doctor for a checkup, many measurements are taken: your height, weight, blood pressure, and heart rate. Even your vision is measured and assigned a number. Blood might be drawn so measurements can be made of lead or cholesterol levels. Measurements quantify our observations: a person’s blood pressure isn’t just “pretty good,” it’s 110/60, the low end of the good range.

What is a measurement? A measurement is a comparison between an unknown quantity and a standard. For example, if you measure the mass of a rolling cart used in an experiment, the unknown quantity is the mass of the cart and the standard is the gram, as defined by the balance or spring scale you use. In the Physics Lab, the length of the spring was the unknown and the centimeter was the standard.
 

Comparing Results

As you learned in previous topics, scientists share their results. Before new data are fully accepted, other scientists examine the experiment, looking for possible sources of error, and try to reproduce the results. Results often are reported with an uncertainty. A new measurement that is within the margin of uncertainty confirms the old measurement.

 

For example, archaeologists use radiocarbon dating to find the age of cave paintings, such as those from the Lascaux cave, in Figure 1-9, and the Chauvet cave. Radiocarbon dates are reported with an uncertainty. Three radiocarbon ages from a panel in the Chauvet cave are

30,940 ± 610 years, 30,790 ± 600 years, and 30,230 ± 530 years. While none of the measurements exactly match, the uncertainties in all three overlap, and the measurements confirm each other.