1. Accuracy: The closeness of a measurement to the true or actual value
Accuracy: The closeness of a measurement to the true or actual value. of what is being measured. BEING RIGHT!
Accurate: Your measurement = 30.5 cm Actual length = 30.5

2. Precision: how SPECIFIC a measurement is
Less Precise More Precise
10 m m m 12 m m m
9 m m m
Groups of measurements that are CLOSE in range to each other = more precise
More SIG. FIGS. = more precise

3. Precise instruments; Precise measurements
Most precise (least estimation)
Least precise (most estimation)

4. Precision Which ruler is the most precise?
Which ruler is not accurate?

5. Precision
Precision of calculated answers is limited by the least precise measurement.
Ex: 2.5 cm cm = 4.75  4.8
Measurements can be precise, but not accurate if an instrument is not calibrated correctly.

6. Precision & Significant Figures
Answers cannot be more precise than the least precise information given
Examples
= 23.72
Answer: 23.7
In + and - : Keep same # of decimal places

7. Answers that Reflect Precision
ADDING OR SUBTRACTING: Answer can only show as many decimal places as the measurement having the fewest number of decimal places.
Example: When we add 3.76 g g g = g
Our final answer is 20.7 g

8. Practice Quizzes on accuracy & precision:
Key Points:
Accuracy – Are your measurements close to the true value?
Precision – Are a group of measurements close to each other or in agreement?
More precise instrumentation leads to greater precision.