12Chapter OneChemicalFoundationsA measurement always has some degreeof uncertainty.the tenths of a pound place; in the second case, the uncertainty occurs in the thousandthsof a pound place. Supposewe weigh two similar grapefruitson the two devices andobtain the following results:BathroomScaleBalanceGrapefruit1Grapefruit21.51b1.51b1.476 Ib1.518 IbUncertainty in measurementis discussedin more detail in Appendix 1.5.Do the two grapefruits have the same mass? The answer depends on which set of resultsyou consider. Thus a conclusion based on a series of measurementsdepends on the cer-tainty of those measurements.For this reason, it is important to indicate the uncertaintyin any measurement.This is done by always recording the certain digits and the first un-certain digit (the estimated number). These numbers are called the significantfigures ofa measurement.The convention of significant figures automaticallyindicates something about the un-certainty in a measurement.The uncertainty
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