science

Unified Code for Units of Measure

Unified Code for Units of Measure is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Unified Code for Units of Measure rather than just read about it. In short: The Unified Code for Units of Measure (UCUM) is a system of codes for unambiguously representing measurement units. Its primary purpose is machine-to-machine communication rather than communication between humans.

Key takeaways

Unified Code for Units of Measure belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Unified Code for Units of Measure to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Unified Code for Units of Measure from memory before moving on to harder problems.

Reference excerpt

The Unified Code for Units of Measure (UCUM) is a system of codes for unambiguously representing measurement units. Its primary purpose is machine-to-machine communication rather than communication between humans. UCUM is used by different organizations like IEEE, and standards like DICOM, LOINC, HL7, and ISO 11240:2012. The code set includes all units defined in ISO 1000, ISO 2955-1983, ANSI X3.50-1986, HL7 and ENV 12435, and explicitly and verifiably addresses the naming conflicts and ambiguities in those standards to resolve them. It provides for representations of units in 7 bit ASCII for machine-to-machine communication, with unambiguous mapping between case-sensitive and case-insensitive representations. A reference open-source implementation is available as a Java applet. There is also an OSGi-based implementation at Eclipse Foundation.

Base units Units are represented in UCUM with reference to a set of seven base units. The UCUM base units are the metre for measurement of length, the second for time, the gram for mass, the coulomb for charge, the kelvin for temperature, the candela for luminous intensity, and the radian for plane angle. The UCUM base units form a set of mutually independent dimensions as required by dimensional analysis. Some of the UCUM base units are different from the SI base units. UCUM is compatible with, but not isomorphic with, SI. There are four differences between the two sets of base units:

The gram is the base unit of mass instead of the kilogram, since in UCUM base units do not have prefixes. Electric charge is the base quantity for electromagnetic phenomena instead of electric current, since the elementary charge of electrons is more fundamental physically. The mole is dimensionless in UCUM, since it can be defined in terms of the Avogadro number, The radian is a distinct base unit for plane angle, to distinguish angular velocity from rotational frequency and to distinguish the radian from the steradian for solid angles.

Metric and non-metric units

Each unit represented in UCUM is identified as either "metric" or "non-metric". Metric units can accept metric prefixes as in SI. Non-metric units are not permitted to be used with prefixes. All of the base units are metric. UCUM refers to units that are defined on non-ratio scales as "special units". Common examples include the bel and degree Celsius. While these are not considered metric units by UCUM, UCUM nevertheless allows metric prefixes to be used with them where this is common practice. Binary prefixes are also supported.

Arbitrary units UCUM recognizes units that are defined by a particular measurement procedure, and which cannot be related to the base units. These units are identified as "arbitrary units". Arbitrary units are not commensurable with any other unit; measurements in arbitrary units cannot be compared with or converted into measurements in any other units. Many of the recognized arbitrary units are used in biochemistry and medicine.

Derived units Any metric unit in any common system of units can be expressed in terms of the UCUM base units.

See also Outline of metrology and measurement GNU Units International vocabulary of metrology

Notes

References

Further reading Schadow, Gunther; McDonald, Clement J.; Jeffrey G., Suico; Föhring, Ulrich; Tolxdorff, Thomas (1999-03-01). "Units of Measure in Clinical Information Systems". Journal of the American Medical Informatics Association. 6 (2): 151–162. doi:10.1136/jamia.1999.0060151. PMC 61354. PMID 10094068.

External links Media related to Unified Code for Units of Measure at Wikimedia Commons unitsofmeasure.org Archived 2012-10-17 at the Wayback Machine - The official UCUM web site. The UCUM Organization Unified Code for Units of Measure (UCUM) at Lister Hill National Center for Biomedical Communications (LHNCBC), U.S. National Library of Medicine (NLM) dimensioned::unit_systems::ucum - Rust The UCUM-LHC Validator and Converter UCUM Web Service (API) "UOMo", Eclipse Foundation (2010) "UCUM", Regenstrief Institute (2008)

Worked examples

Example 1 — a first encounter with Unified Code for Units of Measure

Start with the simplest possible case. Write down what Unified Code for Units of Measure claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Unified Code for Units of Measure before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Unified Code for Units of Measure ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Unified Code for Units of Measure

In research: Unified Code for Units of Measure appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Unified Code for Units of Measure in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Unified Code for Units of Measure is common in secondary-school and first-year university syllabi. It links to neighbouring topics Encodings, International standards, Metrology, so understanding it makes those chapters shorter.
In everyday life: Look for Unified Code for Units of Measure outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Unified Code for Units of Measure in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Unified Code for Units of Measure means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Unified Code for Units of Measure out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Unified Code for Units of Measure in simple terms?

Why does Unified Code for Units of Measure matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Unified Code for Units of Measure?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Unified Code for Units of Measure.