Teach lesson
Do two Boyle runs agree?
Compare two real Boyle runs at matched volumes and decide what repeatability does—and does not—tell us.
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Learning Outcomes
Collect matched readings from two prerecorded 60 mL trials.
Calculate absolute and percentage differences at three matched volumes.
Evaluate repeatability without confusing agreement with proof of accuracy.
Student activity preview
Activity Content
Preview only. In a class session, students can fill in responses and submit their work to the teacher.
Two witnesses to the same phenomenon
6 min
Two people can time the same race and obtain slightly different results. Careful measurements can still differ because of instrument resolution, how the display is read, and small variations in the setup. In the Boyle lab we can test agreement by comparing two separate recorded trials from the same instrument and setup at matched volumes.
Repeatability means a similar measurement appears when the procedure is repeated. It does not by itself prove perfect accuracy, but it increases confidence that a pattern does not depend on one run.
What do you expect when comparing two runs at the same volumes?
Repeat the procedure
19 min
Open the lab twice. Use the 60 mL syringe both times, selecting trial 1 first and trial 2 second. In each trial, record only 60, 40, and 30 mL. The table has one row per volume and separate columns for both trials.
Same instrument, another trial
Read the large pressure number beside kPa—it appears red in the current interface—and confirm the volume before saving it.
Lab-screen note: the introduction may mention pressure and temperature. In this Boyle run, syringe volume changes, pressure is measured, and temperature is treated as approximately constant.
First lab run: trial 1
Open the lab and choose the 60 mL syringe, trial 1.
Record the pressure at 60 mL.
Advance through the pauses until you reach 40 mL and record the pressure again.
Continue to 30 mL and record the third reading.
Second lab run: trial 2
Open the lab again and choose the 60 mL syringe, trial 2.
Record pressures at 60, 40, and 30 mL in the trial-2 column.
For each row, calculate the absolute difference:
|trial 1 P − trial 2 P|. Then calculate the mean pressure andpercentage difference = absolute difference ÷ mean pressure × 100.
Complete exactly three rows. Each row matches the same volume across trials; do not compare different volumes. Calculate with the pressures as displayed and an unrounded mean; round only the mean you report to 0.01 kPa and the final percentage difference to 0.1%. Leave any extra interface row unused.
Comparison of two trials
One row per volume. Copy both pressures, then calculate the absolute difference, mean pressure, and percentage difference.
| Volume mL | Trial 1 pressure kPa | Trial 2 pressure kPa | Absolute difference kPa | Mean pressure kPa | Percentage difference % |
|---|---|---|---|---|---|
Quantify repeatability
9 min
At which volume is the percentage difference largest? State the volume, percentage, and corresponding absolute difference.
Use the 40 mL row as a calculation check: show (P1 + P2) ÷ 2, then absolute difference ÷ mean pressure × 100. Enter the final percentage difference rounded to one decimal place.
For this preliminary classroom check, treat the two runs as showing close agreement only when the unrounded percentage difference is at most 5% at all three tested volumes. Round only the value you report to 0.1%. This is a class decision rule, not a calibration specification.
Do the two trials show close agreement in this preliminary check? Apply the 5% rule to all three rows, cite the largest percentage difference and at least one absolute difference, and explain what the comparison does—and does not—show.
Confidence does not mean perfection
6 min
Close agreement in two runs gives preliminary evidence of repeatability, but does not prove sensor accuracy. Both trials could share a bias, and only three volumes in one configuration were checked.
Write a four-sentence reflection:
1. State whether the runs show close agreement under the 5% rule, and cite the largest percentage difference.
2. Explain why two runs provide only preliminary evidence of repeatability.
3. Explain why that agreement does not establish sensor accuracy.
4. Describe how a third run would strengthen the repeatability test.