scientific unit system

Mathematica: The awesome Quantity system for values with units is everything the SysMLv1.x Quantity/Unit system should have been (and hopefully SysMLv2 will be). But it comes at a high performance cost!

In many English-speaking countries, however, the most common shape of a handwritten Arabic digit 1 is just a vertical stroke; that is, it lacks the upstroke added in many other cultures.

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Webel vs SysPhS-1.1: Annex A.5: Humidifier: Where ValueTypes involving litre are defined, the Unit symbol "L" is used rather than the Modelica-preferred "l" (in combination with an explicit additional unit converter).

In 1990, the International Committee for Weights and Measures stated that it was too early to choose a single symbol for the litre.

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In the UK and Ireland, as well as the rest of Europe, lowercase l is used with prefixes, though whole litres are often written in full (so, "750 ml" on a wine bottle, but often "1 litre" on a juice carton).

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In these countries, the symbol L is also used with prefixes, as in mL and μL, instead of the traditional ml and μl used in Europe.

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The United States National Institute of Standards and Technology now recommends the use of the uppercase letter L, a practice that is also widely followed in Canada and Australia.

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Therefore, the digit "1" may easily be confused with the letter "l". In some computer typefaces, the two characters are barely distinguishable. As a result, L (uppercase letter L) was adopted by the CIPM as an alternative symbol for litre in 1979.

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Originally, the only symbol for the litre was l (lowercase letter L), following the SI convention that only those unit symbols that abbreviate the name of a person start with a capital letter.

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The litre (British English spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm^3), 1000 cubic centimetres (cm^3) or 0.001 cubic metre (m^3).

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Webel vs SysPhS-1.1: Annex A.5: Humidifier: Where custom ValueTypes are defined, Modelica-friendly Unit symbols are used. Examples: "m3" not "m^3"; "degC" not "°C"; "J/(K.L)" (full stop as multiplier) not "J/(K⋅L)"; (EXCEPT "L" for litre not "l").

Webel vs SysPhS-1.1: Annex A.5: Humidifier: Dimensional analysis of VaporPressureCalculationConstraint implies each 1 mL of water is equated with EXACTLY 1 g of produced vapor.

Webel: SysMLv1.x: AVOID (where possible) SysML Unit names that are the same as unit symbols. Unit names SHOULD start with a lower case Latin alpha letter. Custom Unit names should be a single lower case word or lowerCamelCase.

QuantityKind and ValueType example - frequency vs clock frequency vs sound frequency

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Gallery

Tutorial

TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo

Section

08:03: The SysML QuantityKind and Unit

Slide kind

SysML Block Definition Diagram (BDD)

QuantityKind and ValueType example - length vs radius vs radius of tire

This content has been marked as discussing an ADVANCED topic!

Gallery

Tutorial

TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo

Section

08:03: The SysML QuantityKind and Unit

Slide kind

SysML Block Definition Diagram (BDD)

The only valid use of a Unit instance is to be referenced by the unit property of a ValueType stereotype.

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OMG Systems Modeling Language (SysML) 1.6

Two such InstanceSpecifications represent the same "measurement unit" if and only if their definitionURIs have values and their values are equal.

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OMG Systems Modeling Language (SysML) 1.6

The definitionURI of an InstanceSpecification classified by a kind of Unit identifies the particular "measurement unit" [VIM3-1.9] that the InstanceSpecification represents.

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OMG Systems Modeling Language (SysML) 1.6

Modelers specialize Unit as done in SysMLs QUDV model library or in a similar manner in other model libraries.

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OMG Systems Modeling Language (SysML) 1.6

Unit, or a specialization of it, classifies an InstanceSpecification to define a particular "measurement unit" in the sense of a "real scalar quantity, defined and adopted by convention, with which any other quantity of the same kind can be compared ...

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OMG Systems Modeling Language (SysML) 1.6

Unit is defined as a non-abstract SysML Block defined in the SysML UnitAndQuantityKind model library.

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OMG Systems Modeling Language (SysML) 1.6

A unit may also specify less stable or precise ways to express some value, such as a cost expressed in some currency, or a severity rating measured by a numerical scale.

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OMG Systems Modeling Language (SysML) 1.6

A unit often relies on precise and reproducible ways to measure the unit. For example, a unit of length such as meter may be specified as a multiple of a particular wavelength of light.

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OMG Systems Modeling Language (SysML) 1.6

A Unit is a quantity in terms of which the magnitudes of other quantities that have the same quantity kind can be stated.

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OMG Systems Modeling Language (SysML) 1.6

The only valid use of a QuantityKind instance is to be referenced by the quantityKind property of a ValueType or Unit.

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OMG Systems Modeling Language (SysML) 1.6

Two such InstanceSpecifications represent the same "kind-of-quantity" if and only if their definitionURIs have values and their values are equal.

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OMG Systems Modeling Language (SysML) 1.6

The definitionURI of an InstanceSpecification classified by a kind of QuantityKind identifies the particular "kind-of-quantity" [VIM3-1.2] that the InstanceSpecification represents.

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OMG Systems Modeling Language (SysML) 1.6

Modelers specialize QuantityKind as done in SysMLs QUDV model library or in a similar manner in other model libraries.

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OMG Systems Modeling Language (SysML) 1.6

... a SysML value property is understood to correspond to the VIM concept of "quantity" defined as a "property of a phenomenon, body or substance, where the property has a magnitude that can be expressed as a number and a reference" [VIM3-1.1].

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OMG Systems Modeling Language (SysML) 1.6

QuantityKind, or a specialization of it, classifies an InstanceSpecification to define a particular "kind-of-quantity" in the sense of an "aspect common to mutually comparable quantities" [VIM3-1.2], ...

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OMG Systems Modeling Language (SysML) 1.6

QuantityKind is defined as a non-abstract SysML Block defined in the SysML UnitAndQuantityKind model library.

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OMG Systems Modeling Language (SysML) 1.6

A QuantityKind is a kind of quantity that may be stated by means of defined units. For example, the quantity kind of length may be measured by units of meters, kilometers, or feet.

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OMG Systems Modeling Language (SysML) 1.6

SysML ValueType and QUDV overview

Gallery

Tutorial

TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo

Section

08:02: The SysML ValueType, Unit, and using values

Slide kind

SysML Block Definition Diagram (BDD)

QUDV in SysML refers to: Quantity, Unit, Dimension, Value. It is strongly influenced by the International Vocabulary of Metrology (VIM).

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