How to plot a good graph

#truestory

Remember the acronym SLAP

Scale Line Axis Points

Characteristics

First and last points to cover more than half

the graph paper in both directions unless prevented by certain conditions specified in the question

Avoid awkward scales e.g. 2 cm is used to represent 3 units making it impossible to read each small square accurately. Recommended scale – 2 cm to represent 1, 2, 5 units of

the variable (or 0.1, 20, 500 etc). show the area covered by 1st and last points and

indicate at least 6 squares vertically and at least 5 squares horizontally

Scale

Scale

Use sharp pencil to draw thin, neat

and smooth line or curve. Best fit straight line or curve means

Passing through as many points as possible.

Equal points are on either side of line, for points that do not pass through the line.

No point is too far from line or curve. (Except anomalous points)

Line

Extend line beyond first

and last points and the line should be as long as possible.

Use a 30-cm long ruler for practical to draw straight line.

Line

Axes are correctly labelled with

correct physical quantities and units (in solidus notation).

Use more markings to prevent wrong reading of scale.

Plot a graph of Variable 1 (Vertical Axis) against Variable 2 (Horizontal Axis)

Axis

Mark the data points clearly

with neat thin small crosses.

Points must be plotted according to the values in the table. Read the scales carefully.

Points

Calculating the gradient and y-

intercept

#likeaboss

G

rad

ient

The triangle used should cover at

least half of the line drawn. The triangle should be drawn in

dotted line and do not mark the points used with crosses.

Indicate the coordinates to be used. The coordinates must be on the line.

Gradient

Do not use plotted/ data points to

calculate gradient. Use other coordinates.

Show complete working as to how gradient is obtained.

Values read from graph should be according to the number of decimal places of the scales used.

Gradient

Example

(no units for gradient, but units required for R)

Example

Gradient = 1.60

Using y = mx + c,and the coordinates (0.35, 0.75),

0.75 = (1.60)(0.35) + c

c = 0.19