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UT Austin College of Natural Sciences:
UNIT02: Measurement
Prep Materials for College Level Chemistry
Significant Figures (Significant Digits)
If we give 40 people ten Vernier calipers and one line to measure, there is very little
chance that all 40 people will come up with the exact same number for their
measurement. They’ll get things like 4.45, 4.46, 4.43, 4.44, 4.45, etc. So what is the
true measurement? Significant figures help us handle such cases.
Significant figures rules exist for measurements and for computations with
measurements. This section introduces these rules.
The Point: Report only ONE questionable digit for
measurements.
In the example with the Vernier caliper above, everyone agrees on the “4.4” part of
the measurement. The hundredthsplace is the questionable digit.
The Exceptions:
Counting Numbers and Defined Quantities
The Exceptions: Counting numbers are said to have infinite significant digits. That is
to say, if there are three people in the room, no one will say there are 2.999 people
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 Fall '07
 Fakhreddine/Lyon
 Chemistry

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