234 lines
4.8 KiB
Groff
234 lines
4.8 KiB
Groff
.Dd $Mdocdate: May 22 2024 $
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.Dt SI 7
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.Os
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.Sh NAME
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.Nm SI
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.Nd The International System of Units
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.Sh SOURCE
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NIST SP 330,
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.Em The International System of Units (SI) ,
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2019 edition,
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.Lk https://doi.org/10.6028/NIST.SP.330-2019 .
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Some data from the
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.Sx NOT-ACCEPTABLE NON-SI UNITS STILL IN USE
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section are from NIST SP 811,
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.Em NIST Guide for the Use of the International System of Units (SI) ,
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2008,
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.Lk https://www.nist.gov/pml/special-publication-811 .
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The IEC binary prefixes are defined in ISO/IEC 80000-13.
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.Sh PREFIXES
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.TS
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allbox tab( );
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c | c | c || c | c | c
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l c r || l c r.
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Name Prefix Power Name Prefix Power
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quetta Q 30 quecto q -30
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ronna R 27 ronto r -27
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yotta Y 24 yocto y -24
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zetta Z 21 zepto z -21
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exa E 18 atto a -18
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peta P 15 femto f -15
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tera T 12 pico p -12
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giga G 9 nano n -9
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mega M 6 micro \(mc -6
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kilo k 3 milli m -3
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hecto h 2 centi c -2
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deka da 1 deci d -1
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.TE
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.Sh BINARY PREFIXES
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Binary prefixes multiply a unit by a power of 2. They not a part of the
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SI system. Most people will say
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.Dq kilobyte
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instead of
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.Dq kibibyte ,
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.Dq megabyte
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instead of
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.Dq mebibyte ,
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and so on. Mac OSX and Linux utilities commonly report
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units using the binary prefixes
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(
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.Dq KiB ,
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.Dq MiB ,
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etc).
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.TS
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allbox tab( );
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c | c | c
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l c r.
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Name Prefix Power Related
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kibi Ki 10 kilo
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mebi Mi 20 mega
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gibi Gi 30 giga
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tebi Ti 40 tera
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pebi Pi 50 peta
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exbi Ei 60 exa
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zebi Zi 70 zetta
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yobi Yi 80 yotta
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.TE
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.Sh BASE UNITS
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.TS
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allbox;
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r | l | c | c
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r l c c.
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Quantity Unit Symbol Dimension
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time second s T
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length meter m L
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kilogram mass m M
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current ampere A I
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temperature kelvin K \(*H
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luminosity candela cd J
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Unitless = 1 =
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.TE
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Unitless quantities (like indices of refraction) are usually written
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with no symbol at all, or with a conventional symbol, like
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.Dq rad
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(see below).
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.Sh DERIVED UNITS
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.TS
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allbox;
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r | l | c | c | c
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l l c c c.
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Quantity Unit Symbol Base Units Equivalent
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plane angle radian rad m/m 1
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solid angle steradian sr m\(S2/m\(S2 1
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frequency hertz Hz s⁻¹ =
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force newton N kg m s⁻² =
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T{
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pressure, stress
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T} pascal Pa kg m⁻¹ s⁻² N m⁻²
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T{
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energy, work, heat
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T} joule J kg m² s⁻² N m
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T{
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power, radiant flux
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T} watt W kg m² s⁻³ J/s
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T{
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electric potential difference
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T} volt V kg m² s⁻³ A⁻¹ W/A
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charge columb C A s =
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capacitance farad F kg⁻¹ m⁻² s⁴ A² C/V
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resistance ohm \(*W kg m² s⁻³ A⁻² V/A
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conductance siemens S kg⁻¹ m⁻² s³ A² A/V
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T{
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magnetic flux
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T} weber Wb kg m² s⁻² A⁻¹ V s
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T{
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magnetic flux density
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T} tesla T kg s⁻² A⁻¹ Wb m⁻²
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inductance henry H kg m² s⁻² A⁻² Wb/A
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T{
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temperature, celsius
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T} celsius \(de C K + 273.15 =
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T{
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luminous flux
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T} lumen lm cd sr =
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T{
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illuminance
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T} lux cd sr m⁻² lm m⁻²
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T{
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activity referred to a
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radionuclide
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T} becquerel Bq s⁻¹ =
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T{
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absorbed dose, kerma
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T} gray m² s⁻² J/kg
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T{
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dose equivalent
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T} sievert Sv m² s⁻² J/kg
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T{
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catalytic activity
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T} katal kat mol s⁻¹ =
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.TE
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The equivalent units for pressure do not appear in the source.
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.Sh SAMPLE OF OTHER DERIVED UNITS
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.TS
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allbox;
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l r r.
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Quantity Units Base
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dynamic viscosity Pa s kg m⁻¹ s⁻¹
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surface tension N m kg m² s⁻²
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T{
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angular velocity, angular frequency
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T} rad s⁻¹ s⁻¹
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T{
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heat flux density, irradiance
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T} W m⁻² kg s⁻³
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T{
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heat capacity, entropy
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T} J K⁻¹ kg m² s⁻² K⁻¹
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T{
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specific heat capacity, specific entropy
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T} J K⁻¹ kg⁻¹ m² s⁻² K⁻¹
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T{
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thermal conductivity
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T} W m⁻¹ K⁻¹ kg m s⁻³ K⁻¹
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T{
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electric field strength
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T} V m⁻¹ kg m⁻¹ s⁻³ A⁻¹
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permittivity F m⁻¹ kg⁻¹ m⁻³ s⁴ A²
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permeability H m⁻¹ kg m s⁻² A⁻²
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T{
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radiant intensity
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T} W sr⁻¹ kg m² s⁻³
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radiance W sr⁻¹ m⁻² kg s⁻³
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.TE
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The sources give more examples.
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.Sh NON-SI UNITS ACCEPTED FOR USE IN SI
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.TS
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allbox;
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l l c r.
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Quantity Name Sym. Value
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time minute min 1 min = 60 s
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\^ hour h 1 h = 60 min = 3600 s
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\^ day d 1 d = 24 h = 86400 s
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length T{
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astronomical unit
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T} au T{
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1 au = 149 597 870 700 m
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T}
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angle degree \(de 1\(de = (\(*p/180) rad
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\^ minute \(fm T{
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1\(fm = (1/60)\(de = (\(*p/10 800) rad
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T}
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\^ second \(sd T{
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1\(sd = (1/60)\(de = (\(*p/648 000) rad
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T}
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area hectare ha 1 ha = 1 hm² = 10⁴ m²
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volume liter L 1 L = 1 dm³ = 10³ cm³ = 10⁻³ m³
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mass metric ton t 1 t = 10³ kg
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\^ dalton Da 1 Da = 1.660 539 040 (20) E-27 kg
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energy electronvolt eV 1 eV = 1.602 176 634 e-19 J
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T{
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logarithmic quantities
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T} neper Np natural log
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\^ bel B base-10 log
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\^ decibel dB 1 dB = 10⁻¹ B
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.TE
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.Sh NOT-ACCEPTABLE NON-SI UNITS STILL IN USE
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.TS
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allbox;
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l l c r.
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Quantity Name Sym. Value
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length ångström \(oA 10⁻¹⁰ m
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\^ micron \(*m 1 \(*mm
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\^ parsec pc 1 pc = 3.085 678E+16 m
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T{
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radiation dose
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T} rad rad OR rd 1 rd = 10⁻² Gy
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pressure T{
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millimeter of mercury
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T} mmHg 1 mmHg \(=~ 133.322 Pa
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T{
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magnetic flux density
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T} gauss G OR Gs 1 G = 100 μT
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.TE
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.Sh INFO
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This file is public domain. Manual page version 2024.01.
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