Be able to adjust the maximum and minimum values of an axis scale and set incremental values

Topic 16 – Graphs and Charts

Objective

Be able to adjust the maximum and minimum values of an axis scale and set incremental values.

Why Adjust Axis Scales?

Proper axis scaling ensures that data is displayed clearly and that the chart accurately reflects the relationships between data points. In ICT examinations you may be asked to:

• Set a suitable minimum value so that the chart starts at a logical point (e.g., zero for quantities).
• Choose a maximum value that accommodates the highest data point without excessive empty space.
• Define incremental (major) units that make the grid easy to read.

Key Terms

• Minimum value – the lowest number shown on an axis.
• Maximum value – the highest number shown on an axis.
• Increment (major unit) – the step size between successive grid lines or tick marks.
• Minor units – optional smaller steps between major increments.

General Procedure (Applicable to most spreadsheet software)

1. Select the chart to activate the Chart Tools or Format Chart Area pane.
2. Choose the axis you wish to modify (usually the vertical Y‑axis for values).
3. Open the Axis Options dialog.
4. Enter the desired Minimum and Maximum values.
5. Set the Major unit (incremental value).
6. Optionally adjust the Minor unit for finer grid lines.
7. Click OK and review the chart to ensure the data is displayed as intended.

Example Scenario

Suppose you have the following data set representing monthly sales (in £) for a small business:

Month	Sales (£)
January	420
February	560
March	730
April	610
May	890

The highest sales figure is £890. To create a clear column chart you might choose:

• Minimum value: 0 (so the chart starts at zero).
• Maximum value: 1000 (a round number slightly above the highest data point).
• Major unit (increment): 200 (gives grid lines at 0, 200, 400, 600, 800, 1000).

Mathematically, the axis scale can be expressed as:

$$\text{Axis values} = \{0, 200, 400, 600, 800, 1000\}$$

Tips for Choosing Appropriate \cdot alues

• Always include zero as the minimum for quantitative data unless the context specifically requires otherwise (e.g., temperature above freezing).
• Round the maximum up to a “nice” number (multiple of 10, 20, 50, 100) to avoid odd fractions on the axis.
• Pick an increment that results in 5–10 major grid lines – this balances readability and detail.
• If the data range is small, consider using a larger increment and a narrower maximum/minimum range to highlight differences.

Common Pitfalls

• Setting the minimum above zero when zero is a meaningful reference point.
• Choosing an increment that does not divide evenly into the range, causing the final grid line to fall short of the maximum.
• Forcing the software’s automatic scaling without checking whether it obscures trends.

Summary Table

Action	What to consider	Typical choice
Set Minimum	Should reflect logical start point (often 0)	0 or lowest data point rounded down
Set Maximum	Must be ≥ highest data point; round up for neatness	Next round number above max (e.g., 1000 for 890)
Set Increment (Major unit)	Number of grid lines (5‑10) and ease of reading	Range ÷ 5‑8, rounded to a convenient value
Set Minor Unit (optional)	Provides finer reference points	Major unit ÷ 2 or ÷ 5

Practice Exercise

Using the data below, decide on appropriate minimum, maximum and increment values for a line graph. Show your calculations.

Day	Temperature (°C)
Mon	12
Tue	15
Wed	9
Thu	14
Fri	11

Answer format (example):

Minimum = 0°C
Maximum = 20°C
Increment = 5°C

Exam Checklist

1. Identify the highest and lowest data values.
2. Decide whether zero should be included.
3. Round the maximum up to a convenient number.
4. Calculate a suitable major unit (range ÷ 5‑8, then round).
5. Enter the values in the chart’s axis options.
6. Verify that all data points are visible and the grid is easy to read.