Axis Assignment: The independent variable is plotted on the horizontal x-axis, while the dependent variable is plotted on the vertical y-axis. A helpful mnemonic is that the 'independent' variable is a longer word and 'sinks' to the bottom.
Axis Labelling: Similar to table headings, each axis must be labelled with the quantity name or symbol followed by a forward slash and the unit (e.g., ).
Title Structure: A standard scientific title follows the format: 'A graph to show how [Dependent Variable] depends on [Independent Variable]'. This clearly defines the relationship being investigated.
Plotting Technique: Data points should be marked with a small, sharp 'x' rather than a large dot to ensure the exact coordinate is visible and precise.
Space Utilization: A graph should occupy at least 75% of the available grid space. This ensures that the data is spread out enough to allow for accurate gradient calculations and trend identification.
Scale Selection: Scales should be linear and use sensible increments such as 1, 2, 5, or multiples of 10. Avoid awkward scales (like 3 or 7) that make plotting and reading values difficult.
Origin Constraints: While the origin is often included, it is not mandatory unless a y-intercept must be determined directly from the graph. If the data range is far from zero, the axes can start at a more appropriate value.
Line of Best Fit: This line should represent the overall trend of the data, with roughly an equal number of points above and below the line. It should be a single, thin, continuous line drawn with a ruler for linear trends.
| Feature | Tables | Graphs |
|---|---|---|
| Primary Purpose | Recording and organizing raw/processed data. | Visualizing relationships and trends between variables. |
| Variable Placement | Independent on the left; Dependent on the right. | Independent on x-axis; Dependent on y-axis. |
| Precision | Shows exact numerical values and decimal places. | Shows general trends and allows for estimation between points. |
| Labelling Style | Symbol / Unit in column headers. | Quantity / Unit on axis labels. |
The Slash Rule: Always use a forward slash between the quantity and the unit. Writing 'Time (s)' is often acceptable, but 'Time / s' is the standard convention in many physics and chemistry specifications.
Check the 75% Rule: Before drawing your axes, calculate the range of your data and ensure your chosen scale will force the graph to fill most of the page. Examiners often deduct marks for 'postage stamp' sized graphs.
Gradient Triangles: When calculating a gradient, draw a large triangle that covers at least 75% of the line of best fit. This reduces the percentage error in your calculation.
Unit Awareness: Always check if the table or graph uses prefixes (like , , or ) or powers of ten. Forgetting to include these in calculations is a very common source of error.
