Unit 03 · Measurement, Units & Significant Figures
Science runs on numbers, and a number is only as good as the way it was measured. This skill sits after the notebook because now you have an honest place to write measurements down — the next job is making them trustworthy. A student reads a ruler at eye level, records the mass of a paper-towel sample with its unit attached, keeps only the digits the stopwatch actually gives, and times a pendulum’s swing three times to report an average. Mastery means every number you write down means exactly what it says.
| Criterion | Developing | Proficient | Mastery |
|---|---|---|---|
| Reading instruments | Reads from an angle, guesses randomly between the marks, or doesn’t know where the scale starts. | Reads the right tool but looks from above the water line or rounds to the nearest big mark. | Reads ruler, balance, graduated cylinder, and stopwatch at eye level, to the smallest mark the tool offers. |
| Units & conversions | Writes bare numbers with no units; cannot move between centimeters and meters. | Records units most of the time but stumbles converting within the metric system. | Attaches the correct unit to every measurement and converts cleanly between metric units when asked. |
| Significant figures | Copies every digit the calculator shows, inventing precision the tool never had. | Senses that the extra digits are wrong but keeps or drops them inconsistently. | Records exactly the digits the instrument supports — no invented precision, no thrown-away real digits. |
| Precision vs. accuracy | Uses “precise” and “accurate” as if they mean the same thing. | Can define both but cannot say which one a given set of results has. | Tells precision from accuracy and, shown a set of trials, says clearly which one the data shows. |
| Repeat measurement | Measures once and treats that single number as the answer. | Takes a few trials but reports only one, or averages them incorrectly. | Times the pendulum several times and reports the average, noting how close the trials were. |
| Integration (cross-domain) | Makes no supported connection between the source and the science. | Uses the source but needs help connecting evidence, writing, or limitations to the science. | Independently connects History, Reading, and Writing using a cited source, appropriate evidence, a limitation, and a scientific explanation. |
Integration is reported separately and cannot lower the science grade or block a science demonstration pass. Science and practical criteria determine that pass. Use the integration guide's evidence checklist for the separately reported criterion.
“I read the water at the bottom of the curve, right at eye level, so it’s 24.5 milliliters — the cylinder only goes to half a mL, so that’s all the digits I get. I timed the swing three times and averaged them. The trials were close together, so it’s precise; whether it’s accurate depends on if my stopwatch is right.”
“It’s like… 24-ish? The calculator said 24.50000 so I wrote all of that. I only measured it once. Precise and accurate are basically the same thing.”
You demonstrate this unit through watched measurement tasks — reading real instruments and recording what they show — plus short oral checks where you explain your numbers aloud. Not a multiple-choice test. A criterion counts as mastered only when a guide can watch you do it: read at eye level, keep the units, hold to the tool’s precision, and average repeated trials. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.