Accuracy vs. Precision

For each target describe whether the marks areAccurate, Precise, Both, or Neither

The surface of liquids in a glass cylinder is always curved. Thiscurved surface is called a meniscus. When reading a volume of a liquid,read the bottom of the meniscus.

What is the most precise volume of the liquid shown in the figure below?A 19.4 mLB 19.42 mLC 19.57 mLD 20.58 mL

A student measured the length of a piece of string that was 64.34 cm long. Her measurements were 67.02 cm, 67.07 cm, 67.05 cm, and 67.04 cm.

Which of the following statements is true?A The measurements were accurate but not precise.B The measurements were precise but not accurate.C The measurements were both precise and accurate.D The measurements were neither accurate nor precise.

Two students, Garrison and Isabella, determined the mass of an object on two different balances. The accepted mass of the object was 2.355 g. Garrison obtained values of 2.531 g, 2.537 g, 2.535 g and 2.533 g. Isabella obtained values of 2.350 g, 2.404 g, 2.296 g and 2.370 g.

Which statement best describes the results that were obtained by Garrison and Isabella.

(a) Garrison obtained the better accuracy.

(b) Isabella obtained the better accuracy.

(c) Garrison obtained the better precision.

(d) Isabella obtained the better precision.

Precision Problems:A group of students worked in separate teams to measure the length of an object.

Here are their data:

• The average length is ________ cm.This is the mean or average.

• Subtract the highest value from the lowest value: _________ cm.This is the range or spread.

• Divide this number by 2: _______ cm.This is the approximate ± range from the average.

• The precision of the measurement can be shown as average ± range.The precision of the measurement was ________±_____ cm.

Team 1 Team 2 Team 3 Team 4 Team 5 Team 6 Team 7

2.65 cm 2.75 cm 2.80 cm 2.77 cm 2.60 cm 2.65 cm 2.68 cm

A second group of students obtained the following data:

• The average length is ________ cm.

• The precision of the measurement was ________±_____ cm.

In comparing groups, the first or the second, which group was more precise or was the precision the same? Justify your answer.

Team 8 Team 9 Team 10

Team 11 Team 12 Team 13 Team 14

2.60 cm 2.70 cm 2.80 cm 2.75 cm 2.65 cm 2.62 cm 2.78 cm