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The number of divisions on a metric ruler or
meter stick determines how precise the instrument is.
A ruler with millimeters as the smallest division is
more precise than a ruler with centimeters as the smallest division.
Earlier we measured this triangle with a metric ruler whose
smallest division was one millimeter and
determined it was 3.17 centimeters long.
If the same triangle was measured using a metric ruler whose
smallest division is one centimeter,
the measurement would not be as precise.
Length measured with this ruler can be read to
one-tenth of one centimeter.
It has a reading error of plus or minus 0.1 centimeter.
The measurement could be recorded as 3.1 centimeters.
The three can be read directly from the ruler so it is certain.
The one is estimated, so it is uncertain.
3.1 centimeters has two significant figures.
This measurement is not as precise.