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'''“Parts-per” notation''' is used in [[science]] and [[engineering]], to denote proportionalities in measured quantities such as proportions at the parts-per-million ('''ppm'''), parts-per-billion ('''ppb'''), and parts-per-trillion ('''ppt''') level. Since parts-per notations are quantity-per-quantity measures, they are known as ''dimensionless quantities''; that is, they are pure numbers with no associated [[measurement|units of measurement]]. | '''“Parts-per” notation''' is used in [[science]] and [[engineering]], to denote proportionalities in measured quantities such as proportions at the parts-per-million ('''ppm'''), parts-per-billion ('''ppb'''), and parts-per-trillion ('''ppt''') level. Since parts-per notations are quantity-per-quantity measures, they are known as ''dimensionless quantities''; that is, they are pure numbers with no associated [[measurement|units of measurement]]. | ||
==Parts per million== | |||
Parts-per notation is often used in the measure of dilutions ([[concentration]]s) in [[chemistry]]; for instance, for measuring the relative abundance of dissolved minerals or pollutants in water. The expression ''1 ppm '' means a given property exists at a proportion of one part per million parts examined, as would occur if a water-borne pollutant was present at a concentration of one-millionth of a [[gram]] per gram of sample solution. | |||
Similarly, parts-per notation is used also in [[physics]] and [[engineering]] to express the value of various proportions. For example, a metal might expand 1.2 [[micrometre]] per [[metre]] of length for every [[Celsius|degree Celsius]] and this would be expressed as a [[Coefficient of thermal expansion]] of 1.2 ppm/°C. As another example, the accuracy of land-survey distance measurements when using a [[laser rangefinder]] might be 1 millimetre per kilometre of distance and this could be expressed as an accuracy of 1 ppm. | |||
Revision as of 18:23, 9 August 2008
“Parts-per” notation is used in science and engineering, to denote proportionalities in measured quantities such as proportions at the parts-per-million (ppm), parts-per-billion (ppb), and parts-per-trillion (ppt) level. Since parts-per notations are quantity-per-quantity measures, they are known as dimensionless quantities; that is, they are pure numbers with no associated units of measurement.
Parts per million
Parts-per notation is often used in the measure of dilutions (concentrations) in chemistry; for instance, for measuring the relative abundance of dissolved minerals or pollutants in water. The expression 1 ppm means a given property exists at a proportion of one part per million parts examined, as would occur if a water-borne pollutant was present at a concentration of one-millionth of a gram per gram of sample solution.
Similarly, parts-per notation is used also in physics and engineering to express the value of various proportions. For example, a metal might expand 1.2 micrometre per metre of length for every degree Celsius and this would be expressed as a Coefficient of thermal expansion of 1.2 ppm/°C. As another example, the accuracy of land-survey distance measurements when using a laser rangefinder might be 1 millimetre per kilometre of distance and this could be expressed as an accuracy of 1 ppm.