Be able to format numerical values to a specified number of decimal places

Topic 16 – Graphs and Charts

Objective

Be able to format numerical values to a specified number of decimal places.

Why Decimal Formatting Matters

• Ensures consistency across data labels, axis values and tables.
• Improves readability of charts – especially when values are very large or very small.
• Helps avoid mis‑interpretation of data caused by excessive or insufficient precision.

Rounding Rules (to a specified number of decimal places)

When rounding a number to n decimal places, follow these steps:

1. Identify the digit in the n‑th decimal place.
2. Look at the digit immediately to its right (the n+1‑th decimal place).
3. If the n+1‑th digit is 5 or greater, increase the n-th digit by 1.
4. If the n+1-th digit is less than 5, leave the n-th digit unchanged.
5. Discard all digits to the right of the n-th place.

Original \cdot alue	Rounded to 0 dp	Rounded to 1 dp	Rounded to 2 dp	Rounded to 3 dp
12.3456	12	12.3	12.35	12.346
0.0049	0	0.0	0.00	0.005
7.555	8	7.6	7.56	7.555

How to Format Decimal Places in Spreadsheet Software

Microsoft Excel / Google Sheets

1. Select the cells containing the numbers you wish to format.
2. Right‑click and choose Format Cells… (Excel) or click Format → Number → More Formats → Custom number format (Sheets).
3. In the Number category, set the number of decimal places required (e.g., 2).
4. Click OK. The displayed values will now show the chosen precision, while the underlying values remain unchanged.

Using Formulas to Control Decimal Places

Sometimes you need the rounded value for calculations. Use the ROUND function:

$$\text{Rounded \cdot alue} = \text{ROUND}(\text{Number},\ n)$$

where n is the number of decimal places.

Example: =ROUND(A2,2) rounds the value in cell A2 to two decimal places.

Applying Decimal Formatting to Charts

• After formatting the source data, insert or update the chart.
• For axis labels, right‑click the axis, choose Format Axis, and set the Number format to the same decimal places.
• Data labels can be formatted individually by selecting them and choosing Number Format in the label options.

Practice Questions

1. Round the following values to the indicated decimal places and write the result as it would appear on a chart axis:
   • 23.6789 – 0 dp
   • 5.4321 – 1 dp
   • 0.98765 – 3 dp
2. In a spreadsheet, the raw data for a line graph is:

   Month	Average Temperature (°C)
   Jan	4.236
   Feb	5.112
   Mar	7.894

   Apply a format of 1 decimal place to the temperature column. What values will be displayed on the graph?
3. Explain why using too many decimal places on a pie‑chart data label can be misleading.

Summary Checklist

• Identify the required number of decimal places for the chart.
• Use the ROUND function if the rounded value is needed for calculations.
• Apply cell formatting to control displayed precision.
• Update axis and data‑label formats to match the source data.
• Check the chart for readability before finalising.