Significant Digits and Experiments
Dr. MJ Patterson
Now that we have seen how to count the number of sig figs in a reported value, let's look at how to take numbers from experimental measurements in the lab, and report them correctly. The main idea is that you want to report all of the digits that you know with certainty, plus the first digit that you must estimate.
For example, if you use a graduated cylinder that is marked to the nearest mL, you might observe that the liquid inside is between the 42 mL and 43 mL markings. You know with certainty that the measurement is 42 mL. However, you should also estimate the next digit. If it is closer to 42 than 43, you might estimate 42.3 mL. If it is closer to 43, you might estimate 42.8 mL.
In our introductory and general chemistry labs, we commonly use burets. These burets are marked to the tenth mL, or one decimal place. How many decimal places should your reported value have any time you use a buret? Well, since you know with certainty to the nearest tenth, you need to estimate to the nearest hundredth, or 2 decimal places.