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Very low solute concentrations are often expressed using appropriately small units such as parts per million (ppm) or parts per billion (ppb). Like percentage (“part per hundred”) units, ppm and ppb may be defined in terms of masses, volumes, or mixed mass-volume units.
- 2.1 Essential data
- 2.1.1 Tables and graphs
- 3.2 Fundamental Constants Data Center
- SI base unit Base quantity
- SI coherent derived unit Derived quantity
- Name
- Symbol
- 5 Units Outside the SI
- 5.1 Units accepted for use with the SI
- 5.1.4 Natural and atomic units
- Kind of quantity
- 5.3 Units not accepted for use with the SI
- 5.3.1 CGS units
- 6.1 Rules and style conventions for unit symbols
- 6.1.2 Capitalization
- 6.2 Rules and style conventions for SI prefixes
- 6.2.1 Typeface and spacing
- 6.2.2 Capitalization
- 6.2.4 Unacceptability of compound prefixes
- 7.12 Proper names of quotient quantities
- 7.13 Distinction between an object and its attribute
- 7.14 Dimension of a quantity
Essential data express or interpret quantitative results. All such data shall be given in acceptable units. In those cases where — the sole use of acceptable units would compromise good communication, or — units other than acceptable units have been specified as a contractual requirement, values of quantities shall be given in acceptable units fo...
In tables, values of quantities expressed in acceptable units and the corresponding values expressed in other units may be shown in parallel columns, with the acceptable-unit column preceding the other-unit column. In graphs, axes labeled in other units shall be given secondary status. This may preferably be done by placing scale marks on and label...
Questions concerning the more fundamental aspects of the SI and subtle aspects of proper SI usage may be directed to:
length mass time electric current thermodynamic temperature amount of substance luminous intensity
area volume speed, velocity acceleration wavenumber density, mass density specific volume current density magnetic field strength luminance amount-of-substance concentration amount concentration , concentration
square meter cubic meter meter per second meter per second squared reciprocal meter kilogram per cubic meter cubic meter per kilogram ampere per square meter ampere per meter candela per square meter mole per cubic meter
dynamic viscosity moment of force surface tension angular velocity angular acceleration heat flux density, irradiance heat capacity, entropy specific heat capacity, specific entropy specific energy thermal conductivity energy density electric field strength electric charge density surface charge density electric flux density, electric displ...
Units that are outside the SI, that is, non-SI units, may be divided into three categories: — those units that are accepted for use with the SI by the CIPM and hence this Guide; — those units that are not accepted for use with the SI by the CIPM, but are temporarily accepted for use with the SI by this Guide; and — those units that are not accept...
The following four sections discuss in detail the units this Guide accepts for use with the SI.
In some cases, particularly in basic science, the values of quantities are expressed in terms of fundamental constants of nature. The two most important of these unit systems are the natural unit (n.u.) system used in high energy or particle physics, and the atomic unit (a.u.) system used in atomic physics and quantum chemistry. The use of these un...
speed action mass electric charge length energy time
The following two sections briefly discuss units not accepted for use with the SI.
Table 10 gives examples of centimeter-gram-second (CGS) units having special names. These units are not accepted for use with the SI by this Guide. Further, no other units of the various CGS systems of units, which includes the CGS Electrostatic (ESU), CGS Electromagnetic (EMU), and CGS Gaussian systems, are accepted for use with the SI by this Gui...
The following eight sections give rules and style conventions related to the symbols for units.
Unit symbols are printed in lower-case letters except that: the symbol or the first letter of the symbol is an upper-case letter when the name of the unit is derived from the name of a person; and the recommended symbol for the liter in the United States is L. (See Table 6, footnote (b).) Examples: m (meter) Pa (pascal) s (second) lm (lumen) ...
The following eight sections give rules and style conventions related to the SI prefixes.
Prefix names and symbols are printed in roman (upright) type regardless of the type used in the surrounding text, and are attached to unit symbols without a space between the prefix name or symbol and the unit name or symbol. This last rule also applies to prefixes attached to unit names. Examples: mL (milliliter) pm (picometer) GΩ (gigaohm) THz ...
The prefix symbols Y (yotta), Z (zetta), E (exa), P (peta), T (tera), G (giga), and M (mega) are printed in upper-case letters while all other prefix symbols are printed in lower-case letters (see Table 5). Prefix names are normally printed in lowercase letters.
Compound prefix names or symbols, that is, prefix names or symbols formed by the juxtaposition of two or more prefix names or symbols, are not permitted. Example: nm (nanometer) but not: mμm (millimicrometer)
Derived quantities formed from other quantities by division are written using the words “divided by” or per rather than the words “per unit” in order to avoid the appearance of associating a particular unit with the derived quantity. Example: pressure is force divided by area or pressure is force per area but not: pressure is force per unit area
To avoid confusion, when discussing quantities or reporting their values, one should distinguish between a phenomenon, body, or substance, and an attribute ascribed to it. For example, one should recognize the difference between a body and its mass, a surface and its area, a capacitor and its capacitance, and a coil and its inductance. This means t...
Any SI derived quantity Q can be expressed in terms of the SI base quantities length (l ) , mass (m), time (t), electric current (l ) , thermodynamic temperature (T ) , amount of substance (n), and luminous intensity (Iv) by an equation of the form K
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Definition. Parts per million (ppm) and parts per billion (ppb) show a relationship between two quanti-ties that use the same units. A part per million could be one drop per one million drops, one gram per one million grams, etc. By definition, one ppm = 1,000 ppb.
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Aug 24, 2019 · Related concentration units are parts per thousand (ppth), parts per million (ppm) and parts per billion (ppb). Parts per thousand is defined as follows: \[ppth\: =\: \frac{mass\: of\: solute}{mass\: of\: sample}\times 1000\]
Jun 15, 2020 · Parts per million (ppm) and parts per billion (ppb) are ratios that give the grams of solute in, respectively, one million or one billion grams of sample. For example, a sample of steel that is 450 ppm in Mn contains 450 μg of Mn for every gram of steel.
They are abbreviations for the words parts-per-million, parts-per-billion, and parts-per-trillion. These symbols have become commonplace in everyday use, in the media for example, as well as in scientific and technical contexts.
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Parts per million and parts per billion are used to describe concentrations of highly dilute solutions. These measurements correspond to milligrams and micrograms of solute per kilogram of solution, respectively.
