Chapter 2 of 8

Scales, Lettering & Dimensioning

In the DSSSB AE Civil syllabus under Engineering Graphics · 2 parts

Scales & Dimensioning · Drawing Instruments, Standards, Lines & Lettering

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📑 Contents (12 sections)

Part 1 of 2

Scales & Dimensioning

Last reviewed 16 Sept 2026 · 8 min read

Scales

Objects are often too large (buildings, bridges) or too small (watch parts) to be drawn full size. A scale is the ratio of the size of the drawing to the actual size of the object.

FormulaRepresentative fraction

R F = \frac{length on drawing}{actual length of object} (same units)

Length of scale $= R F \times$ maximum length to be measured

Type of scale	RF	Examples
Full-size scale	= 1	1 : 1
Reducing scale	< 1	1 : 2, 1 : 100
Enlarging scale	> 1	2 : 1, 10 : 1

Recommended scales (SP 46)

Enlargement: 50 : 1, 20 : 1, 10 : 1, 5 : 1, 2 : 1
Full size: 1 : 1
Reduction: 1 : 2, 1 : 5, 1 : 10, 1 : 20, 1 : 50, 1 : 100, 1 : 200, 1 : 500, 1 : 1000, 1 : 2000, 1 : 5000, 1 : 10 000

Typical uses in civil engineering: building plans 1 : 100 (or 1 : 50), details 1 : 20, 1 : 10, 1 : 5, site plans 1 : 500 or 1 : 1000, layout/location plans 1 : 2000 or smaller.

The scale must always be stated in the title block; if a drawing may be enlarged or reduced during reproduction, a graphic (bar) scale is drawn on the sheet.

Types of scales

Scale	Features
Plain scale	Divided into main units and first sub-units (e.g. metres and decimetres) — reads two units
Diagonal scale	Uses diagonals to read three units (e.g. metres, decimetres and centimetres) — based on similar triangles; accurate small subdivisions
Vernier scale	A main scale and a sliding/auxiliary vernier scale; reads small fractions of the smallest main scale division — forward (direct) or backward (retrograde) vernier
Comparative scales	Two scales with the same RF but different units (e.g. km and miles)
Scale of chords	Marks angles by chord lengths — used when a protractor is not available
Map scales	Expressed as RF (1 : 50 000), statement ("1 cm = 0.5 km") or graphic bar scale

Construction of a plain scale (steps)

Compute RF and length of scale.
Draw a line of that length; divide it into the required main units.
Divide the first main division (at the left) into sub-units.
Mark zero at the end of the first main division; number main units to the right and sub-units to the left.
Draw the scale as a thin rectangle (commonly about 10 mm wide), write the RF and units below.

Construction of a diagonal scale (principle)

If a short length $P Q$ is to be divided into $n$ parts, draw a perpendicular $QR$ of any length, divide it into $n$ equal parts, join $P$ to $R$ , and draw lines parallel to $P Q$ through the division points. The $k$ -th parallel line cut by the diagonal has length $\frac{k}{n} P Q$ .
Thus, sub-units are subdivided further by 10 equal vertical divisions and diagonals.

Vernier scale

FormulaLeast count

Least count = 1 MSD - 1 VSD = \frac{1 MSD}{n}

(forward vernier: $n$ vernier divisions = $(n - 1)$ main scale divisions)

Backward vernier: $n$ vernier divisions = $(n + 1)$ main scale divisions; LC = 1 VSD − 1 MSD.

Part 2 of 2

Drawing Instruments, Standards, Lines & Lettering

Last reviewed 16 Sept 2026 · 7 min read

Engineering drawing

Engineering drawing is the graphic language of engineers — a precise, standardised way of communicating the shape, size, material and construction details of objects and structures. Unlike artistic drawing, it follows standards so that it is interpreted uniformly.

In India, engineering drawing practice is standardised by the Bureau of Indian Standards in SP 46 (Engineering Drawing Practice for Schools and Colleges), which is based on ISO standards. IS 962 deals with architectural and building drawings.

Drawing instruments and materials

Instrument / material	Use
Drawing board	Flat wooden board with a straight working edge; sizes such as D0, D1, D2 to suit sheet sizes
Mini-drafter	Clamped to the board; two perpendicular scales with a protractor head — draws horizontal, vertical and inclined lines quickly (replaces T-square, set squares and protractor)
T-square	Horizontal parallel lines (used against the board edge)
Set squares	45° and 30°–60° triangles — vertical and inclined lines; combined to draw lines at 15° intervals
Protractor	Measuring and setting angles
Scales	Plastic/boxwood scales with different reduction ratios; engineer's scale set
Large compass	Circles and arcs (with lengthening bar for large radii)
Bow compass	Small circles and arcs
Dividers	Transferring distances and dividing lines into equal parts
French curves	Drawing irregular (non-circular) curves smoothly through plotted points
Templates / stencils	Circles, ellipses, symbols, lettering
Pencils	Grades from 9H (hardest) to 9B (softest); H = hard, B = black/soft, HB = medium. Typically 2H/H for construction lines, H/HB for finished lines, HB for lettering
Clutch/mechanical pencils	Constant line width (0.3, 0.5, 0.7 mm leads)
Erasers and erasing shield	Clean removal of selected lines
Drawing clips / adhesive tape	Fixing the sheet
Sandpaper block	Sharpening pencil leads (conical or chisel point)

Drawing sheets

Sizes (ISO A-series, trimmed sizes)

Designation	Size (mm)
A0	841 × 1189
A1	594 × 841
A2	420 × 594
A3	297 × 420
A4	210 × 297

A0 has an area of 1 m²; each smaller size is obtained by halving the longer side of the previous size.
Sides are in the ratio 1 : √2, which is preserved on halving.

Layout of a drawing sheet

Borders — a wider margin (commonly about 20 mm) on the left edge for filing/binding, and narrower margins (commonly about 10 mm) on other sides.
Title block — at the bottom right-hand corner, containing name of institution/organisation, title of drawing, drawing number, scale, projection symbol, date, names/signatures (drawn, checked, approved), sheet number and revisions.
Revision table, parts list (for assemblies) above the title block.
Folding marks and grid reference system on large sheets.
Orientation — sheets used in landscape or portrait as convenient; title block always readable in the normal viewing direction.

Lines

Types of lines (SP 46 / ISO)

Line	Description	Applications
A	Continuous thick	Visible outlines and edges
B	Continuous thin (straight)	Dimension lines, extension (projection) lines, leader lines, hatching (section lines), short centre lines, imaginary lines of intersection
C	Continuous thin freehand	Short break lines, limits of partial views
D	Continuous thin with zigzags	Long break lines
E / F	Dashed (thick / thin)	Hidden outlines and edges
G	Chain thin (long dash–dot)	Centre lines, lines of symmetry, trajectories, pitch circles
H	Chain thin, thick at ends and at changes of direction	Cutting planes (section planes)
J	Chain thick	Surfaces with special requirements (e.g. heat treatment)
K	Chain thin double-dashed	Outlines of adjacent parts, alternative/extreme positions of moving parts, centroidal lines

Line thickness and precedence

Two thicknesses are used, with thick lines about twice the thickness of thin lines (e.g. 0.5 mm and 0.25 mm, or 0.7 mm and 0.35 mm).
Order of precedence when lines coincide: visible outline > hidden line > cutting plane line > centre line > projection/dimension lines.
Dashes of hidden lines and chain lines should be uniform; centre lines should extend slightly beyond the outline and cross at long dashes, not at gaps.
A hidden line meeting a visible line should start with a dash touching it (or a gap where it continues the visible line).

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