http://www.ck12.org Chapter 1. What Is Science?
18.26. But this isn’t true. The way to state the measurement and include the precision of the ruler is to write 18.00.
Reading 18.00 informs us that the measurement appears exactly at the 18 cm mark but is also capable of measuring
one more digit to the right with certainty, and estimating yet another digit to the right. The measurement 18.00 has
four significant figures, while the measurement 18 has only two significant digits.
FIGURE 1.
An example of a ruler where the units
place is an estimate.Zero as a Placeholder
A United States penny has a diameter of 1.91 cm as measured with our ruler. Even though the ruler can measure
lengths like 11.91 cm, the penny has no “tens of centimeter” value. You can’t measure what is not there, so there
is no added “significance” if we write a zero in front of the ones-units to indicate there are no tens, like this: 01.91.
This number has only three significant figures. The zero is not a measure of anything and the diameter of the penny
is in the range [1.86 - 1.96] cm.
FIGURE 1.
A penny cannot be measured to the “tens-
place” so zero in the “tens-place” is only a
place holder and has no significance.Check Your Understanding
- How many significant digits are there in: