Engineering Graphics, Standards and Visual Communication

Introduction

Engineering drawing is the graphical language used to communicate the form, size, function, manufacture, installation, inspection and maintenance of an engineering product or system. Unlike artistic illustration, an engineering drawing is not primarily intended to be attractive; it is intended to be unambiguous, measurable and verifiable. A correctly prepared drawing allows designers, analysts, manufacturers, electricians, inspectors and maintenance personnel to interpret the same technical intention.

For electrical engineers, engineering graphics is relevant to circuit diagrams, wiring layouts, printed-circuit-board documentation, control-panel layouts, electrical installation plans, cable schedules, equipment arrangements, earthing systems and power-system schematics. Although computer-aided design (CAD) is now dominant, CAD software does not replace graphical knowledge. A technically incorrect drawing remains incorrect whether it is produced with a pencil or a sophisticated software package.

Standards provide the common rules that make drawings transferable between organizations and countries. ISO standards are widely used internationally; IEC standards are particularly important for electrotechnical documentation; ANSI standards are prominent in the United States. National standards may adopt, modify or supplement these international systems. The designer must therefore identify the governing standard before beginning a drawing.

Learning Objectives

By the end of this chapter, the student should be able to:

1. Explain engineering drawing as a technical language.
2. Distinguish sketches, detail drawings, assembly drawings, diagrams and schematics.
3. Select suitable sheet sizes, drawing scales and title-block information.
4. Apply standard line types, lettering, dimensioning principles and symbols.
5. Explain the roles of ISO, IEC, ANSI and national standards.
6. Interpret drawing conventions used in electrical and general engineering documentation.
7. Identify common causes of ambiguity and propose methods for preventing drawing errors.
8. Prepare and check a simple standards-compliant engineering drawing.

1. Engineering Drawing as a Technical Language

A language requires vocabulary, grammar and rules for interpretation. Engineering graphics has the same structure:

• Vocabulary: lines, symbols, views, dimensions, notes, section marks and abbreviations.
• Grammar: rules governing projection, line hierarchy, dimension placement, notation and symbol use.
• Standards: formally agreed rules that control the meaning and presentation of graphical information.
• Context: the discipline, application, manufacturing process and intended users.

An engineering drawing should communicate five related types of information:

A drawing is effective when a competent user can obtain the required information without guessing. Ambiguous graphical representation can cause incorrect manufacture, unsafe installation, equipment failure and costly rework.

1.1 Types of engineering representation

A freehand sketch is a rapidly produced, usually informal representation used to develop or communicate an idea. It may not be to scale, but it should preserve important relationships.

A detail drawing describes one component and contains sufficient information for its manufacture or inspection.

An assembly drawing shows how several components fit together. It may include item numbers, a bill of materials and assembly notes.

A general arrangement drawing shows the overall spatial arrangement of equipment, supports, access zones and interfaces.

A diagram emphasizes function or relationships rather than physical appearance. A circuit diagram, block diagram and control diagram are examples.

A schematic diagram uses standardized symbols and connecting lines to represent functional connections. The physical location of components is often deliberately omitted.

A layout drawing represents the actual or intended physical location of equipment, conductors, terminals or components.

The distinction between a schematic and a layout is essential in electrical engineering. A schematic may show that a protective device is electrically upstream of a load, while a layout shows where the device is physically mounted in a panel.

2. Standardization and the Drawing Environment

Standardization reduces variation in technical communication. It defines not only symbols but also sheet sizes, line conventions, projection methods, tolerances, documentation procedures and revision practices.

2.1 Major standards organizations

ISO (International Organization for Standardization) publishes international standards covering technical product documentation, geometrical tolerancing, paper sizes, line conventions and many other subjects. ISO standards commonly use first-angle projection in many regions, although the projection method must always be identified on the drawing.

IEC (International Electrotechnical Commission) develops international standards for electrical, electronic and related technologies. IEC publications address graphical symbols for diagrams, reference designations, electrotechnical documentation, safety and equipment requirements.

ANSI (American National Standards Institute) coordinates voluntary consensus standards in the United States. In engineering drawing practice, ANSI-related conventions are often encountered together with ASME standards, particularly for dimensioning and tolerancing.

National standards bodies publish standards applicable to a particular country. Examples include BSI in the United Kingdom, DIN in Germany, BIS in India and JIS in Japan. A national standard may adopt an ISO or IEC standard or define national implementation requirements.

Standards are not interchangeable merely because their objectives are similar. For example, symbol shape, projection convention, dimensioning style or reference designation may differ. A drawing should state the applicable standard, such as an ISO, IEC, ANSI/ASME or national standard reference.

2.2 Standards hierarchy in practice

A project may be governed by several layers of requirements:

1. Statutory regulations and safety law.
2. Contract specifications and client requirements.
3. National or regional codes.
4. International or industry standards.
5. Organizational drafting procedures.
6. Project-specific conventions.

Where requirements conflict, the designer must resolve the conflict through the responsible engineering authority rather than silently choosing a preferred convention. The drawing may include a general note such as “Unless otherwise specified, this drawing shall be interpreted in accordance with [identified standard].”

3. Drawing Sheets, Zones and Title Blocks

3.1 Standard sheet formats

The ISO A-series is widely used for technical documentation. The principal sheet sizes are:

The dimensions follow a useful geometric principle: each successive format is obtained by halving the longer side of the preceding format while retaining the same aspect ratio. The ideal ratio is √2:1. This permits drawings to be enlarged or reduced without changing their proportions.

The drawing border provides a controlled working area. Margins allow filing, trimming and handling. Larger sheets may be divided into zones using letters and numbers so that locations can be referenced precisely, for example, “terminal table in zone C4.”

3.2 Orientation and layout

Portrait or landscape orientation is selected according to the shape and information density of the drawing. Views should be arranged to support rapid interpretation. Unnecessary empty space, overcrowding, crossing dimensions and excessively long leader lines reduce readability.

A drawing may contain a drawing area, notes area, revision area, approval area and title block. The layout should be consistent throughout a project so users can find information quickly.

3.3 The title block

The title block is the administrative identity of the drawing. Typical fields include:

• Organization and project name
• Drawing title
• Drawing or document number
• Sheet number and number of sheets
• Revision status
• Scale or “not to scale” statement
• Projection symbol
• Units
• Applicable standards
• Prepared, checked and approved by
• Dates and signatures or electronic approvals
• Material, where relevant
• Confidentiality or document classification

A title block is not decorative. It establishes traceability and supports configuration control. A drawing without a unique number or revision status can lead to the use of obsolete information in manufacture or installation.

3.4 Revision control

A revision identifies a controlled change. A revision record should state the revision identifier, date, description of change and responsible person or authority. Changes should be marked using revision clouds, delta symbols or another project-approved method when appropriate.

A new revision does not necessarily mean that every feature has changed. It means that the controlled document has been modified and reissued. Superseded drawings should be withdrawn from active work areas or clearly marked as obsolete.

4. Lines, Lettering and Graphic Hierarchy

4.1 Line types

Line conventions allow a two-dimensional drawing to represent three-dimensional form and hidden information. Common line types include:

Line thickness should be selected as a coordinated set rather than independently. Visible outlines normally require stronger visual emphasis than construction, dimension and centre lines. A drawing with all lines equally heavy is difficult to read.

Line conventions vary slightly among standards and disciplines. The drawing standard and organizational manual should therefore be consulted for exact patterns and thickness ratios.

4.2 Lettering

Technical lettering must be legible, consistent and reproducible. Important properties include uniform height, spacing, stroke width, inclination and capitalization. Modern CAD systems provide standardized fonts, but the user must still select a font that remains clear when printed or viewed at reduced size.

Text should not overlap lines or obscure symbols. Notes should be concise and should use unambiguous technical terms. Abbreviations should be standardized within the project and defined when they are not universally understood.

4.3 Use of colour and layers

Traditional engineering drawings are generally interpretable in monochrome. Colour may be used in CAD for layers, status or discipline coordination, but critical meaning should not depend on colour alone because drawings may be printed in black and white or viewed by users with colour-vision deficiency.

CAD layers can separate dimensions, construction geometry, electrical conductors, equipment, annotations and revision marks. Layer names, line weights and visibility rules should be controlled by a template. Hidden geometry should not be shown merely because it exists in the CAD model; it should be displayed only when it aids interpretation.

5. Scale and Proportion

Scale expresses the relationship between a dimension on a drawing and the corresponding true dimension. It is commonly written as:

where S is the scale ratio, L_d is the drawing length and L_r is the real or actual length. Both lengths must use the same units.

For a scale of 1:2, the drawing is half the actual size. For 2:1, the drawing is twice the actual size. A scale of 1:1 is full size.

Worked example: selecting a scale

A panel is 1200 mm wide. The available drawing width is 300 mm. The maximum practical scale ratio is:

A scale of 1:4 fits the panel width exactly, before allowing for margins and annotations. In practice, a smaller scale such as 1:5 may be selected to provide space for dimensions and notes.

Scale must not be inferred from measurement alone. Dimensions written on the drawing govern, and drawings should normally include a statement of scale. Details that require enlargement may use a separate detail view such as “DETAIL A, SCALE 2:1.”

In electrical schematics, scale often has no geometric significance. A schematic should then be marked “NTS” or “not to scale,” while maintaining logical and functional clarity.

6. Projection and Views

Projection is the method by which three-dimensional objects are represented on two-dimensional surfaces. The principal systems used in engineering drawing include orthographic projection, axonometric projection, oblique projection and perspective projection.

6.1 Orthographic projection

Orthographic projection uses projectors perpendicular to the viewing plane. Separate views—front, top, side and sometimes sectional views—describe the object accurately without perspective distortion.

The arrangement of views depends on the projection convention. In first-angle projection, the object is conceptually placed between the observer and the projection plane; in third-angle projection, the projection plane is conceptually placed between the observer and the object. The projection symbol must be shown when there is any possibility of confusion.

A view should be selected because it contributes information, not merely because it is customary. Hidden lines should be minimized when a sectional view or auxiliary view communicates the feature more clearly.

6.2 Sectional views

A sectional view represents an object as if part of it has been cut away. Section lining, or hatching, indicates the cut surface. Hatching is usually thin, evenly spaced and inclined, but adjacent components may use different directions or spacing to distinguish them.

Section views are especially useful for housings, bearings, cable glands, switchgear and mechanical interfaces. In electrical drawings, a section may reveal conductor routing, insulation layers or enclosure construction.

7. Dimensioning, Tolerances and Notes

Dimensions communicate size and location. A dimension generally consists of a numerical value, dimension line, extension lines and, where necessary, arrowheads or terminators.

Good dimensioning follows several principles:

• Dimension each required feature once, unless repetition is necessary for a specific purpose.
• Place dimensions where they can be read without ambiguity.
• Avoid dimensioning to hidden lines where a visible reference is available.
• Use a common datum for related locations when functional accuracy depends on that datum.
• Do not scale the drawing to obtain an unlabelled dimension.
• Keep dimensions outside the object where practical.
• State units clearly, especially when more than one unit system may be encountered.

A dimension without a tolerance is incomplete when variation affects fit, safety or function. A tolerance defines the permitted variation from the nominal value. For a bilateral tolerance, a dimension may be written as 20 ± 0.1 mm. This means the acceptable range is 19.9 mm to 20.1 mm, assuming the notation is interpreted in millimetres.

For a nominal dimension with unequal limits, the upper and lower deviations should be stated explicitly. Geometrical tolerances control form, orientation, location or run-out and require a datum reference system where applicable. Detailed tolerancing is governed by the adopted ISO GPS or ANSI/ASME system and should not be improvised.

Electrical drawings also use ratings and labels that function as technical dimensions of performance: voltage, current, frequency, power, interrupting rating, conductor size and protection class. These values must be consistent with the applicable electrical code and equipment specification.

8. Symbols and Electrical Documentation

Symbols compress information into a recognizable graphical form. A symbol is useful only when its meaning is standardized or explicitly defined. Electrical documentation commonly includes symbols for sources, switches, fuses, circuit breakers, relays, motors, transformers, lamps, connectors, earth connections and measuring instruments.

IEC graphical symbols are widely used internationally. National and industry-specific symbol systems may also be encountered. A project should not mix symbol conventions without stating the governing practice.

8.1 Schematic conventions

In a schematic:

• Conductors are represented by lines.
• Junctions should be shown clearly, often by a filled connection dot where the convention requires it.
• Crossing lines must be distinguishable as connected or unconnected.
• Components should have unique reference designations, such as Q1 for a switching or protective device, K1 for a relay, M1 for a motor or T1 for a transformer, according to the adopted standard.
• Signal or power flow should follow a consistent direction where practical.
• Supply rails and reference points should be clearly identified.
• Terminal numbers and wire numbers should correspond to schedules and physical documentation.

A schematic is not a substitute for a wiring diagram. The former emphasizes function; the latter emphasizes point-to-point connections and installation.

8.2 Reference designations and cross-references

Unique identifiers connect different documents. A motor labelled M1 on a schematic should also be labelled M1 on the layout, terminal diagram, cable schedule and bill of materials. Cross-references reduce commissioning and maintenance errors.

A reference designation should not be reused after a component is deleted unless project configuration rules explicitly permit it. Historical identifiers may be retained to preserve traceability.

9. Visual Communication and Information Design

Engineering communication is affected by visual hierarchy. The reader should be able to identify the object, locate important features, distinguish primary from secondary information and trace relationships.

Useful practices include:

• Use line weight to distinguish visible geometry from supporting information.
• Align related views and tables.
• Group notes by subject.
• Use whitespace to separate functional regions.
• Avoid crossing leaders and conductors.
• Keep text orientation consistent.
• Place symbols so their connections can be followed naturally.
• Use detail views when a region becomes crowded.
• Apply consistent naming across all project documents.

A drawing should be checked at its intended output size. A symbol that appears clear on a large monitor may become unreadable when printed on A4 paper. Electronic drawings should also be tested at common zoom levels and in a format that preserves vector quality and searchable text where appropriate.

10. A Standards-Based Drawing Workflow

A disciplined workflow reduces both graphical and engineering errors.

Step 1: Establish requirements

Identify the purpose, users, deliverable format, governing standards, units, required approvals and interfaces with other documents.

Step 2: Select the representation

Decide whether the requirement calls for a sketch, schematic, layout, detail drawing, assembly drawing, single-line diagram, wiring diagram or combination of documents.

Step 3: Set up the template

Choose sheet size, orientation, border, zones, title block, units, projection method, layers, line weights and text styles.

Step 4: Construct the primary information

Create the main views, functional symbols or layout geometry first. Establish datums, reference designations and major relationships before adding secondary notes.

Step 5: Add dimensions and annotations

Dimension functional requirements, identify materials and ratings, add notes and reference relevant standards. Avoid unnecessary duplication.

Step 6: Perform technical checking

Check geometry, connections, ratings, clearances, tolerances, symbol meanings and consistency with calculations and specifications.

Step 7: Perform document checking

Check title-block data, revision history, sheet numbering, spelling, units, scale, projection symbol, approval status and file naming.

Step 8: Issue and control

Export using an approved format, protect the issued file, record the revision and distribute it through the project document-control system.

11. Illustrative Case: Control Panel Documentation

Background

A university laboratory is developing a small motor-control panel containing a three-phase motor, isolator, protective device, contactor, overload relay, start and stop push-buttons, indicator lamps and an emergency-stop circuit. The panel must be manufactured and later maintained by personnel who did not design it.

Problem

An initial drawing shows the components but does not identify terminals, conductor numbers, protective ratings or the relationship between the schematic and the physical panel. Two conductors cross without clear junction indications, and the title block does not state the revision.

Analysis

The drawing fails as a controlled technical document even though an experienced designer may infer the intended circuit. The absence of terminal references makes wiring verification difficult. Ambiguous crossings create a safety risk. Missing ratings prevent a reviewer from checking whether the selected protective devices are appropriate. Lack of revision information creates a risk that an outdated drawing will be used.

Approach and solution

The documentation is divided into four coordinated sheets:

1. A functional schematic showing supply, protection, control logic and motor connections.
2. A terminal and wiring diagram showing point-to-point conductors and terminal numbers.
3. A panel layout showing physical locations, access clearances and cable-entry points.
4. A bill of materials identifying component designations, descriptions and ratings.

IEC-based symbols are selected and identified in the drawing notes. Components receive unique designations: Q1 for the isolating/protective device, K1 for the contactor, F1 for the overload function where the project convention permits, M1 for the motor and S1/S2 for control switches. The schematic and layout use the same designations. All conductors receive wire numbers, and every terminal is identified.

The title block states the sheet number, revision, units, applicable standards, projection convention where relevant and approval status. A review verifies that the motor rating, protective device rating, conductor size and emergency-stop operation agree with the design specification and applicable electrical regulations.

Outcome

The revised documentation can be used independently by the manufacturer, installer, inspector and maintenance technician. The schematic explains operation, the wiring diagram supports construction, the layout supports assembly and the bill of materials supports procurement. The documents are traceable because all sheets carry a common project identity and revision.

Learning points

The case demonstrates that engineering graphics is a systems activity. Correct symbols alone do not guarantee a reliable drawing. Successful documentation requires consistent standards, coordinated identifiers, controlled revisions and checking by people who represent different stages of the product life cycle.

12. Technology, CAD and AI-Assisted Documentation

CAD systems improve accuracy, reuse, editing, layering, parametric control and document coordination. Libraries of approved symbols and templates can reduce repetitive work, but they must be governed. A symbol library may contain outdated or incorrectly defined symbols, and automated defaults may use a standard that differs from the project requirement.

Building information modelling, electrical design databases and product lifecycle management systems extend the drawing from a static sheet into a structured information model. This supports automatic schedules, cross-references and change propagation, but it also increases the importance of data integrity.

AI-assisted tools may help generate draft layouts, detect missing references, compare revisions, identify symbol inconsistencies or extract information from drawings. They must not be treated as the engineering authority. Human review remains necessary because an AI system may misinterpret a symbol, fail to recognize a project-specific convention or produce a visually plausible but unsafe connection.

Digital files also require governance. Access control, version history, file integrity, metadata, backup, cybersecurity and long-term readability are part of engineering document management. A signed or approved PDF may be the official issued document even when the editable CAD file remains under controlled organizational access.

13. Challenges, Limitations and Professional Responsibility

Standards improve consistency but do not eliminate judgment. Different standards may coexist, legacy drawings may use obsolete conventions and international projects may involve multiple languages and unit systems. Designers must identify assumptions and communicate them explicitly.

A drawing can be geometrically accurate but functionally wrong. It can also be functionally correct but unsafe because it omits a protective measure, clearance, warning or rating. Engineers therefore have a professional responsibility to consider public safety, maintainability, accessibility, environmental conditions and regulatory compliance.

Plagiarism and unauthorized copying are additional concerns. Symbols and standards may be publicly recognizable, but project drawings, proprietary layouts, manufacturer data and controlled documents may be protected by copyright, confidentiality or contractual restrictions. Engineers should use licensed content and preserve document security.

Best-Practice Checklist

Before issuing a drawing, confirm that:

• The purpose and intended users are clear.
• The governing standards and units are identified.
• Sheet size, border, zones and title block are complete.
• The drawing number and revision are unique and current.
• Projection method and scale are stated where applicable.
• Line types, symbols, lettering and abbreviations are consistent.
• Dimensions, tolerances, ratings and notes are sufficient.
• Electrical references agree across schematics, layouts and schedules.
• Connections and junctions are unambiguous.
• No critical information depends only on colour.
• The document has been independently checked and formally approved.
• Superseded versions are controlled.

Chapter Summary

Engineering drawing is a standardized technical language for communicating geometry, dimensions, function, manufacture, installation and maintenance. Its vocabulary includes lines, symbols, views, dimensions, notes and reference designations; its grammar is established by projection, dimensioning, layout and documentation rules.

ISO, IEC, ANSI and national standards provide common conventions, but the applicable standard must be identified rather than assumed. Sheet formats, borders, zones and title blocks support readability and document control. Line types create graphic hierarchy, while scale establishes the relationship between drawing and actual size. Orthographic projection communicates form; schematics communicate function; layouts communicate physical arrangement.

Electrical documentation depends especially on standardized symbols, unique reference designations, clear junctions, terminal identification and coordination among schematics, wiring diagrams, layouts and schedules. CAD and AI tools can improve productivity, but professional judgment, checking, safety review and revision control remain essential. A high-quality drawing is not merely attractive: it is accurate, unambiguous, traceable and fit for its intended engineering purpose.

Key Terms

Engineering drawing: A standardized graphical representation used to communicate engineering information.

Technical language: A controlled system of symbols, conventions and rules used for precise communication.

Sketch: A rapidly produced representation, often freehand, used to develop or explain an idea.

Detail drawing: A drawing that provides information for manufacturing or inspecting one component.

Assembly drawing: A drawing showing how components fit and operate together.

Schematic: A functional representation using symbols and connections rather than physical appearance.

Layout drawing: A representation of the physical location of components or equipment.

Standard: An agreed technical rule or specification for consistent practice.

Title block: The controlled identification and administrative information area of a drawing.

Revision: A controlled change to an issued document.

Scale: The ratio of drawing size to actual size.

Orthographic projection: A projection method using projectors perpendicular to the viewing plane.

Sectional view: A view showing internal features as though part of an object were cut away.

Datum: A reference point, line or plane from which dimensions or locations are established.

Tolerance: The permitted variation from a specified nominal value.

Line convention: A standardized use of line form and thickness to convey meaning.

Reference designation: A unique identifier assigned to a component or item.

IEC symbol: A graphical symbol defined or widely used within electrotechnical standardization.

Document control: The process of identifying, approving, distributing and revising technical documents.

Review Questions

Short Answer Questions

1. Why is engineering drawing described as a technical language?
2. State two differences between a schematic and a layout drawing.
3. What information is normally included in a title block?
4. Define drawing scale and explain the meaning of 1:2.
5. Why are revision records important?

Long Answer Questions

1. Explain the roles of ISO, IEC, ANSI and national standards in engineering documentation.
2. Describe the principal line types used in engineering drawing and explain their purposes.
3. Discuss the relationship among orthographic views, sectional views and projection conventions.
4. Explain the principles of dimensioning and the importance of tolerances.
5. Describe a complete workflow for producing and issuing an electrical engineering drawing.

Analytical / Application Questions

1. A panel layout is clear on a CAD screen but becomes unreadable when printed on A4 paper. Analyze the likely causes and propose corrective actions.
2. A wiring diagram contains two crossing conductors, but it is unclear whether they are connected. Explain how the drawing should be revised and what related documents should be checked.
3. A project team uses ISO-based symbols on the schematic and a different national convention on the wiring diagram without stating either standard. Evaluate the risks and recommend a document-control solution.

Multiple Choice Questions with Answers

Question 1

Which drawing type primarily emphasizes the functional relationships among electrical components?

A. Schematic diagram

B. Panel layout

C. Detail drawing

D. Assembly drawing

Correct Answer: A. Schematic diagram

Question 2

What is the scale ratio when a 1200 mm object is represented by a 300 mm drawing length?

A. 1:2

B. 1:3

C. 1:4

D. 4:1

Correct Answer: C. 1:4

Question 3

Which sheet format has nominal dimensions of 210 × 297 mm?

A. A2

B. A3

C. A4

D. A5

Correct Answer: C. A4

Question 4

Which line type is commonly used for a centre line or axis?

A. Continuous thick line

B. Dashed thin line

C. Chain thin line

D. Freehand thick line

Correct Answer: C. Chain thin line

Question 5

What is the principal purpose of a title block?

A. To provide shading for the drawing

B. To identify and control the document

C. To replace all dimensions

D. To show only hidden edges

Correct Answer: B. To identify and control the document

Question 6

Which organization is particularly associated with international electrotechnical standards?

A. IEC

B. ISO only

C. ANSI only

D. A national tax authority

Correct Answer: A. IEC

Question 7

A dimension written as 20 ± 0.1 mm permits which range, assuming the notation is in millimetres?

A. 19.0 to 21.0 mm

B. 19.9 to 20.1 mm

C. 20.1 to 20.2 mm

D. 19.1 to 20.9 mm

Correct Answer: B. 19.9 to 20.1 mm

Question 8

What is the main purpose of a unique reference designation such as M1?

A. To indicate the drawing scale

B. To identify a component consistently across documents

C. To specify paper size

D. To show line thickness

Correct Answer: B. To identify a component consistently across documents

Question 9

Which statement best describes a drawing marked NTS?

A. It must be printed at full size

B. It uses only third-angle projection

C. Its geometry should not be measured to infer dimensions

D. It contains no technical information

Correct Answer: C. Its geometry should not be measured to infer dimensions

Question 10

Why should an AI-generated or automatically produced drawing receive human engineering review?

A. Automation cannot create any lines

B. A visually plausible drawing may still contain unsafe or incorrect technical information

C. Standards prohibit all CAD use

D. Human review is needed only for choosing paper colour

Correct Answer: B. A visually plausible drawing may still contain unsafe or incorrect technical information