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.