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Science · Original worked example

Read the axes before interpreting the trend

Read an original science graph, compare measured values, and separate an observed pattern from an unsupported causal claim.

By Raise Your ACT · Updated October 27, 2026 · How we review content

Before you begin

Useful foundation: Read a numbered scale and subtract two values with the same units.

Your goal: Use a graph’s labels, scale, and measured points to answer a precise comparison question.

Identify what each axis measures and its units. Locate the requested values before interpreting a pattern. A measured association alone does not establish its cause.

Work through an example

In a controlled lamp setup, a sensor measured current at four light levels: 20% → 2 mA, 40% → 5 mA, 60% → 8 mA, and 80% → 11 mA.
Sensor current at four measured light levelsLight levels of 20, 40, 60, and 80 percent correspond to currents of 2, 5, 8, and 11 milliamperes. The same values appear in the table below.02468101220%40%60%80%Lamp light level (%)Current (mA)
Original illustrative data, not a report of a real experiment.
Measured values shown in the graph
Light levelCurrent
20%2 mA
40%5 mA
60%8 mA
80%11 mA
  1. The horizontal axis is lamp light level in percent. The vertical axis is sensor current in milliamperes (mA).
  2. At 40% light, current is 5 mA. At 80%, it is 11 mA.
  3. The increase between those measured points is 11 − 5 = 6 mA. Keep the units in the answer.
  4. The observed pattern is increasing current at the measured light levels. These data do not show what happens above 80% or explain the sensor’s physical mechanism.

Try a question yourself

Using the same measured points, how much does current increase from 20% to 60% light?

Choose an answer, then check your reasoning. This public practice is not saved.

Read all answer explanations

8 mA: 8 mA is the final reading. The question asks for the increase from the starting reading of 2 mA.

10 mA: Adding 2 and 8 does not find the change. Subtract the initial value from the final value.

6 mA — correct answer: Yes. Current rises from 2 mA to 8 mA, an increase of 8 − 2 = 6 mA.

40 mA: 40 is the difference in light-level percentage points. The requested quantity is current, in mA.

What to do next

Compare two series on a graph, then practice distinguishing a measurement from an explanation of why it occurred.

Revisit the idea in a week using a different question. Repeating this example can help you understand it, but remembering its answer is not evidence of learning a new problem.

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These original practice examples are independent of ACT and are not official test questions.