Presenting practical data

1. Definition

Presentation of data and observations (PDO) means organising readings and processed quantities so that another person can identify variables, units, precision and trends without guessing.

2. Key Ideas

• Put the quantity or symbol and unit in each table heading using solidus notation, such as t/s.
• Keep raw readings from the same instrument at consistent decimal places.
• Give calculated values to precision justified by the least precise raw data.
• Place the independent variable on the horizontal graph axis.
• Use simple linear scales that occupy most of the grid.
• Draw the requested best-fit line or curve; do not automatically join experimental points dot to dot.
• Use a large triangle on the best-fit line for a gradient.

3. Detailed Explanations

A. Build the table before measuring

For a pendulum investigation, useful headings are:

Units belong in headings, not repeatedly in data cells. Put raw readings before processed results so the calculation can be checked.

B. Choose and label graph axes

Write quantity and unit on each axis. Choose intervals based on 1, 2 or 5 multiplied by a power of ten where possible. The scale need not start at zero unless the question or physical reasoning requires it, but it must be uniform and easy to read.

Plot small crosses or fine circled dots. Experimental scatter usually calls for a balanced best-fit line or curve. Exact successive motion values may instead require consecutive connections; follow the question wording.

C. Calculate a gradient defensibly

Choose two widely separated points on the drawn line, preferably not the original measured points. Mark a right-angled triangle and write:

gradient = Δ y/Δ x.

Carry the axis units through the calculation. If extension in centimetres is plotted against force in newtons, the gradient unit is cm/N.

D. Treat anomalies transparently

Circle or identify a suspected anomalous point only when it departs clearly from the overall pattern. Recheck or repeat it if possible. Do not erase inconvenient data or force the best-fit line through every point.

4. Common Mistakes

• Writing a unit in the table body but not in its heading.
• Mixing decimal places within one raw-data column.
• Using awkward scale intervals such as 3 or 7 per major square.
• Drawing large blobs that hide the plotted coordinate.
• Joining scattered points dot to dot.
• Calculating the gradient from a small triangle or from two points not on the line.
• Reporting a unitless gradient when the axes carry units.

5. Exam Tips

After plotting, check the first and last point against both scales. For a straight best-fit line, look for a reasonable balance of points on both sides across the entire range, not only in the middle.

6. Worked Examples

7. Mind Stretchers

8. Practice and next step

Redraw one untidy data table and one graph using this checklist. Then continue to Analysis, Conclusions and Evaluation.