Noun
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(chemistry) a substance that changes color to indicate the presence of some ion or substance
can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction
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a device for showing the operating condition of some system
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a signal for attracting attention
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a number or ratio (a value on a scale of measurement) derived from a series of observed facts
can reveal relative changes as a function of time
- index number