T&P Terminology

Question 1

1. Define accuracy.
2. Define error.

Answer 1

Accuracy: the closeness of agreement between a measurement and the true value.

Error: the difference between a measurement and the true value.

Accuracy cannot be quantified, whereas error can. True value = that which would have been obtained in an ideal measurement.

Question 2

Define precision.

Answer 2

The closeness of agreement between independent measurements obtained under the same conditions.

Question 3

Define uncertainty.

Answer 3

The interval within which the true value can be considered to lie with a given level of probability.

Question 4

Give the formula for percentage uncertainty.

Answer 4

100 x uncertainty / measurement

Question 5

A measuring instrument has increments of magnitude x. What the uncertainty in a single reading?

Answer 5

x/2

Question 6

A burette has 0.1 cm³ increments.

1. What is the uncertainty in each measurement?
2. To how many decimal places should readings be recorded?

Answer 6

• 0.05 x 2 = 0.1 cm³
• Two decimal places, the second figure being either 0 or 5

Uncertainty is doubled since you take two readings to get one measurement