science

Reference dimension

Reference dimension 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 Reference dimension rather than just read about it. In short: A reference dimension is a dimension on an engineering drawing provided for information only. Reference dimensions are provided for a variety of reasons and are often an accumulation of other dimensions that are defined elsewhere (e.g. on the drawing or other related documentation).

Key takeaways

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

Reference excerpt

A reference dimension is a dimension on an engineering drawing provided for information only. Reference dimensions are provided for a variety of reasons and are often an accumulation of other dimensions that are defined elsewhere (e.g. on the drawing or other related documentation). These dimensions may also be used for convenience to identify a single dimension that is specified elsewhere (e.g. on a different drawing sheet). Reference dimensions are not intended to be used directly to define the geometry of an object. Reference dimensions do not normally govern manufacturing operations (such as machining) in any way and, therefore, do not typically include a dimensional tolerance (though a tolerance may be provided if such information is deemed helpful). Consequently, reference dimensions are also not subject to dimensional inspection under normal circumstances. Reference dimensions are commonly used in CAD software along with constraints that usually denote the opposite: mandatory dimensions to be precisely followed.

Notation In computer-aided design (CAD) it is commonly used to denote dimensions.

REF Prior to use of modern CAD software, reference dimensions were traditionally indicated on a drawing by the abbreviation "REF" written adjacent to the dimension (typically to the right or underneath the dimension). However, standard ASME Y14.5 has changed the way references are marked, and the abbreviation "REF" has been replaced with the use of parentheses () around the dimension. As an example, a distance of 1500 millimeters might be denoted by (1500 mm) instead of 1500 mm REF. This implementation has followed in modern CAD software that makes use of parentheses as the default denotation method whenever reference dimensions are "automatically" created by the software. The method for identifying a reference dimension (or reference data) on drawings is to enclose the dimension (or data) within parentheses.

See also Engineering drawing abbreviations and symbols Geometric dimensioning and tolerancing ASME Y14.5

References

External links Y14.5 Dimensioning and Tolerancing, 2018, ASME

Worked examples

Example 1 — a first encounter with Reference dimension

Start with the simplest possible case. Write down what Reference dimension 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 Reference dimension 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 Reference dimension 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 Reference dimension

In research: Reference dimension 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 Reference dimension 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: Reference dimension is common in secondary-school and first-year university syllabi. It links to neighbouring topics Technical drawing, so understanding it makes those chapters shorter.
In everyday life: Look for Reference dimension 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 Reference dimension in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Reference dimension 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 Reference dimension out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reference dimension in simple terms?

Why does Reference dimension 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 Reference dimension?

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 Reference dimension.