 ## Rulers and Significant Figures

In this video we’re going to use a ruler
to measure an object to the correct number of significant figures. Before we begin, let’s look at the marks
or graduations that are printed on the ruler. Notice that there are large marks for centimeters
and small marks for millimeters printed on the ruler. Since we have marks for millimeters, we’re
going to be able to measure to the nearest millimeter and then we’re going to be able
to estimate one digit better than that. Since there are ten millimeters in one centimeter,
the large number 1 that you see here represents ten millimeters or one centimeter. The small marks in between the large marks
represent millimeters – as you can see, our object falls somewhere between 12 and
13 millimeters. We are allowed to estimate the position in
between 12 and 13 millimeters. In this case, a good estimate might be somewhere
around 12.6 or 12.7 millimeters; therefore, we can estimate to the nearest tenth of a
millimeter. In this case, our measurement will have three
significant figures. Now let’s look at the same object measured
with a different ruler. On this ruler we only have marks for centimeters,
that means we can estimate the position between one and two centimeters. Since the object doesn’t quite reach the
halfway point in between one and two centimeters, we would estimate this object is somewhere
around 1.3 to 1.4 centimeters. Notice that when we have fewer marks we have
fewer significant figures. When you are ready to make a measurement in
the lab, you are going to have to decide – based on your ruler – how many significant figures
you are going to need to record.