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ASME Y15.1M-1979 — Illustrations for Publication and Projection
📊 ASME Y15.1M-1979 (approved as American National Standard ANSI Y15.1M-1979) is an illustration-preparation specification written primarily for authors and engineers. Its single purpose is to help them prepare legible, effective illustrations with the least effort — illustrations that can serve both publication (periodicals, books, reports, and other printed matter) and projection (conference slides and transparencies). The standard traces its ancestry to the 1949 consolidation of ASA Z15.1-1932 (charts for lantern slides) and Z15.3-1943 (graphs for publication) into the Y15.1 committee; the first edition was published as ASA Y15.1-1959, and this 1979 revision supersedes it. Published under the secretariat of the American Society of Mechanical Engineers (ASME) as part of the ANSI Y15 series on preferred practice for the preparation of graphs, charts, and other technical illustrations, it quantifies legibility using the well-understood laws of optics and human perception.
💡 An illustration is a visual aid and should be designed as such: its purpose is to convey ideas, and it is neither more nor less important than the accompanying words. How well an author prepares printed or projected illustrations usually determines their effectiveness and acceptance.
1. Scope and General Framework 📌
This Standard presents brief, categorical rules for preparing the two classes of illustrations that make up the bulk of technical communication: line drawings and photographic illustrations. Illustrations prepared according to these rules will be legible and effective when normally projected or printed. More detailed recommendations for specific cases are given in other standards of the Y15 series.
Key terms are defined precisely. “Publication” includes periodicals, books, reports, or other printed matter. “Slide” refers to a standard full-frame 35 mm transparency (22.9 mm × 34.2 mm aperture area) or other transparencies used for overhead projection, such as super slides (38 mm × 38 mm aperture area) and viewgraph transparencies (125 mm × 175 mm, 175 mm × 175 mm, and 175 mm × 225 mm aperture areas). These definitions fix the copy size and lettering requirements for original artwork.
⚠️ An existing drawing made for another purpose is rarely satisfactory for projection or publication. Publication space and projection conditions impose finite limits on the relative sizes of the original, its lettering, and its line work. These limits are matters of optics, they are quantitatively known, and the entire Standard is built on them.
2. Intelligent Planning Comes First 🧠
Chapter 3 of the Standard stresses that intelligent planning is important. Before starting, decide what the illustration is to accomplish:
- Purpose: What feature of the message must the illustration convey, and to an audience with what interests, needs, and technical background?
- Necessity: Will the illustration convey the idea more clearly and forcibly than words?
- Form: Which type portrays the idea best — line drawing, photograph, bar chart, table, or other? A simple line sketch may beat a detailed shop drawing; a graph may beat a table.
- Concentration: An illustration should concentrate on one particular point; supporting data, tables, equations, and other nonessential details should be omitted because explanatory clutter detracts from the main emphasis.
The Standard advises not to delay preparing illustrations, since they often require more preparation time than their equivalent in text. Before submitting to a technical journal, examine a recent copy to learn its customary illustration sizes, line weights, lettering sizes, and illustration types — most publishers supply instructions on request. Confer with the publisher before preparing book illustrations.
3. Standard Sizes, Lettering, and Layout 📏
Chapter 4 provides the standard sizes for illustration originals and lettering (Table 1). A typical original has an overall width of 150 mm with a work area of 100 mm × 150 mm, lettered in No. 120 capitals or equivalent. Copy proportions of 2:3 fit standard slide masks and common projection screen shapes. The Standard’s drafting rules include: use only open-grid paper (commercial fine-line papers are unsatisfactory); use double-weight ruling to emphasize the curve; keep the minimum number of grid lines and never let grid lines cut through data symbols or lettering; place all scale numbers and titles outside the grid border; where feasible, omit legends or symbol keys and use curve or data-point labels (callouts); use template or transfer lettering rather than freehand symbols.
| Format | Aperture Size (mm) | Typical Use | Preparation Notes |
|---|---|---|---|
| Standard 35 mm slide | 22.9 × 34.2 | Conference projection | 2:3 composition; short titles outside the graph border |
| Super slide | 38 × 38 | Projection with more content | Square aperture; larger lettering |
| Viewgraph transparency | 125 × 175 / 175 × 175 / 175 × 225 | Presentations, training | Printed or hand-lettered; heavier lines |
| Journal/book original | work area ≈ 100 × 150 | Print reproduction | No. 120 capitals or equivalent; publisher rules take precedence |
💡 The lettering numbering principle: a “200-size” letter is one that remains legible after the largest common reduction of the illustration. All lettering on a figure should meet at least that baseline size — enlarge rather than leave any lettering thinner than the legibility floor.
4. Final Copy, Legibility Testing, and Photographic Illustration 🖼️
Chapter 6, “Preplanning Final Copy,” directs the author to lay out the finished artwork on twice-size or three-times-size guide forms so that the reduced product meets the required clarity; the Standard shows a twice-size final draft for publication or projection. Chapter 7 introduces a legibility test chart: before delivery, verify that after the intended reduction the smallest lettering and finest line work remain readable in projection or print; if not, enlarge or thicken them.
Chapter 8 covers drafting instructions, including standard lines and symbols drawn at three-times size. Chapter 9 addresses photographic illustrations: photographs should be mounted on a flapped board carrying the required information (figure number, captions, etc.) so the reproduction shop and reviewers handle them without creases, and so all necessary data travels with the print.
🚨 The most common failures are using fine-line graph paper, hand-drawn symbols, grid lines running through data points, titles and scale numbers squeezed inside the frame, and lettering too small to survive reduction — all of which degrade legibility sharply in projection or print. Compare your figure against the Standard’s poor-illustration and good-illustration examples before submission.
5. Engineering Practice Essentials 🛠️
- 🔍 Plan before drawing: state the purpose → choose the right form (drawing, photo, bar chart, table) → set lettering size and line weight for the final reduction ratio.
- 📏 Standardize the copy size: use the 100 mm × 150 mm work area (or any 2:3 proportion) so the same artwork can be reused for slides, journal figures, and reports with predictable scaling.
- 🖨️ Design for the final medium: for dual-purpose figures, follow the dual-use rules — titles outside the border for slides, captions after the figure number for publication.
- 🔎 Verify legibility: a reduced proof (printed or projected at the true reduction ratio) is the last quality gate and should be done before delivery.
- 📋 Coordinate with the publisher: obtain the target journal’s figure instructions in advance to avoid rework.
6. Frequently Asked Questions ❓
❓ Q: Why does the Standard insist that an existing drawing made for another purpose is rarely satisfactory?
A: Projection and printing impose well-defined reduction ratios on original size, lettering, and line weight (they are matters of optics). Reusing a figure drawn for a different medium usually leaves lettering too large or too small and lines too fine or too heavy to meet the required final legibility.
A: Projection and printing impose well-defined reduction ratios on original size, lettering, and line weight (they are matters of optics). Reusing a figure drawn for a different medium usually leaves lettering too large or too small and lines too fine or too heavy to meet the required final legibility.
❓ Q: What does a lettering size number mean, and how is it applied on the original?
A: The size number denotes the smallest letter height that remains legible after the figure is reduced to its final size. Work at twice-size or three-times size, scaling lettering and line widths up by the same factor so the reduced result never falls below that minimum.
A: The size number denotes the smallest letter height that remains legible after the figure is reduced to its final size. Work at twice-size or three-times size, scaling lettering and line widths up by the same factor so the reduced result never falls below that minimum.
❓ Q: How do the 35 mm slide and modern viewgraphs relate?
A: The Standard groups full-frame 35 mm transparencies (22.9 × 34.2 mm), 38 × 38 mm super slides, and 125 × 175/175 × 225 viewgraph formats under one “slide” definition with aperture-specific layout rules. In today’s presentation software this maps to setting a 4:3 or square slide size and enforcing a minimum legible font size.
A: The Standard groups full-frame 35 mm transparencies (22.9 × 34.2 mm), 38 × 38 mm super slides, and 125 × 175/175 × 225 viewgraph formats under one “slide” definition with aperture-specific layout rules. In today’s presentation software this maps to setting a 4:3 or square slide size and enforcing a minimum legible font size.
🔍 Q: What exactly does Table 1 of the Standard specify?
A: Table 1 specifies “standard sizes for illustration originals and lettering”: the size steps for the original copy (for example, 150 mm overall width with a 100 × 150 mm work area) together with the matching lettering size (No. 120 capitals or equivalent). The two must be used together to guarantee legibility after reduction.
A: Table 1 specifies “standard sizes for illustration originals and lettering”: the size steps for the original copy (for example, 150 mm overall width with a 100 × 150 mm work area) together with the matching lettering size (No. 120 capitals or equivalent). The two must be used together to guarantee legibility after reduction.
