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 | Not yet | Approaching | Mastered |
|---|---|---|---|
| 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) | Treats measuring as isolated; makes no connection to the year’s anchor. | Mentions Semmelweis’s numbers but cannot link honest measurement to his death-rate comparison. | Connects careful counting and rate measurement to Semmelweis — whose ward death rates only meant something because they were measured the same way — across History · Reading · Statistics, and defends why honest numbers decide the case. |
“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.