1.29 Significant Figures
Now look at the graduated cylinder sketched below. How much blue liquid does it contain? First, it’s important to
note that you should read the amount of liquid at the bottom of its curved surface. This falls about half way between
the mark for 36 mL and the mark for 37 mL, so a reasonable estimate would be 36.5 mL.
Q:How many significant figures does this measurement have?
A:There are three significant figures in this measurement. You know that the first two digits (3 and 6) are accurate.
The third digit (5) is an estimate.
Rules for Counting Significant Figures
The examples above show that it’s easy to count the number of significant figures when you are making a measure-
ment. But what if someone else has made the measurement? How do you know which digits are known for certain