Unit #1Unit #2Unit #3Unit #4Unit #5Unit #6Unit #7Unit #8Unit #9Unit #10
spacerUNIT # 1  
spacerspacerIntroduction
spacerspacerObjectives
spacerspacerReading

spacer1.1
Metric
spacerSystem
spacerSI System
spacerBritish System

spacer1.2 Temperature
spacerMeasure-
spacerments

spacer1.3 Scientific
spacerNotation

spacer1.4 Dimensional
spacerAnalysis

spacer1.5 Precision,
spacerAccuracy,
spacerUncertainty

spacerLimitation of the Measuring Instrument
spacerAnalysis of the Limitation of a Ruler
spacerAnalysis of the Limitation of another Ruler
spacer1.6 Significant
spacerFigures

spacerThe Magnitude and Reliability of the Measurement
spacerFive Rules for Determining the number of Significant Figures in a Measurement

spacer1.7 Calculations
spacerInvolving
spacerSignificant
spacerFigures
spacerRules for Rounding off Numbers
spacerRules for Addition  and Subtraction

spacerRules for Multiplication and Division

spacer1.8 Density
spacerDensity and Temperature
spacer1.9 Specific
spacerGravity
spacerspacerProblems
spacer1 | 2 | 3
   

MEASUREMENT

1.5 - Precision, Accuracy and Uncertainty


1.5.2 - Analysis of the Limitation of a Ruler

The diagram below shows the measurement of the length of a blue bar using a ruler with 1 cm as its finest division.

Using this ruler, the length the blue bar is recorded to be 2.3 cm. In Section 1.6, you will learn that this measurement has 2 significant figures.

Let's analyze this measurement:

  1. Upon inspection of the ruler, we observe that the finest division is a 1 cm division.
  2. We can always make an estimate of a reading to within the finest division. Therefore, to the best of my judgement, I conclude that this particular ruler is able to provide a reading accuracy to +/- 0.2 cm. (Note: A plus or minus 0.2 cm reading accuracy means that a length measurement using this ruler will contain uncertainty in the first decimal place.)
  3. The end of the blue bar is between the 2 cm and the 3 cm mark. We can estimate that the blue bar exceeds 2 cm mark by approximately 0.3 cm.
  4. The length measurement is determined to be 2.3 cm.
    The digit '2' is a certain figure. The digit '3' is an uncertain figure, or an estimate in the measurement. Therefore, this length measurement has 2 significant figures. (Note: This measurement is accurate to 2.3 +/- 0.2 cm (i.e. 2.3 plus or minus 0.2 cm). It means that using this ruler, the length of the blue bar is between 2.1 cm to 2.5 cm.)
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