Accuracy &
Precision
Tuesday, August 25th, 2015
Accuracy vs Precision –
Accuracy – how close a measurement is to
the actual value
Precision – how close a group of
measurements are to each other.
Look at each target below and decide whether the
situation is accurate, precise, both, or neither:
(note-it is “accepted” that the bull’s eye is the place everyone aims for.)
Percent Error - how close a measured value is to
its actual value (aka accuracy).
A student takes an object with an accepted (actual)
mass of 200.00 grams and masses it on his own
balance. He record the mass as 196.5 g. What is his
percent error?
How accurate do you need to be....+/- 10%
Practice Problems
1. An experimental measurement was taken of
10.4 mL and the actual measurement was 9.7
mL. What is the percent error?
2. Joe measured the volume of an object five
times and got results of 34.5 mL, 34.9 mL, 34.2
mL, 33.4 mL, and 35.9 mL. The actual volume of
the object was 34.1 mL. What was the percent
error of his average result?
3. A student measured the temperature of boiling
water and got 97.5°C. What was her percent
error?
Practice Problems
1. An experimental measurement was taken of
10.4 mL and the actual measurement was 9.7
mL. What is the percent error?
% error = | 9.7 – 10.4 | x 100 = 7.2%
9.7
Practice Problems
2. Joe measured the volume of an object five
times and got results of 34.5 mL, 34.9 mL, 34.2
mL, 33.4 mL, and 35.9 mL. The actual volume of
the object was 34.1 mL. What was the percent
error of his average result?
34.5 + 34.9 + 34.2 + 33.4 + 35.9 = 172.9/5
= 34.6 mL
% error = | 34.1 – 34.6 | x 100 = 1.47%
34.1
Practice Problems
3. A student measured the temperature of boiling
water and got 97.5°C. What was her percent
error?
% error = | 100°C – 97.5°C | x 100 = 2.50%
100 °C