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Ruler Game
A measurement practice app at /Measurement/. Students see a length (for example 1 3/16″)
and a 6″ ruler. They slide across the ruler, and a green bar fills behind the cursor, snapping to
the nearest visible mark. Clicking records the answer.
- Correct: the bar flashes green, the score for that answer is shown, and the next problem loads automatically.
- Incorrect: the bar flashes red. Then a gold bar shows the correct length, with a red mark where the student clicked. It stays until the student presses Next.
On a touchscreen, students drag along the ruler and lift their finger to answer. Keyboard users can move with the arrow keys (one mark at a time) or Page Up/Down (one inch), then press Enter.
A How to play panel below the game explains the controls, scoring and tiers. It starts open; if a student collapses it, it stays collapsed on that device.
Every student starts at Tier 1. Each tier adds either a new size of fraction to measure or a harder ruler.
| Tier | Lengths asked | Smallest mark on the ruler | Fraction labels |
|---|---|---|---|
| 1 | whole inches | 1/4″ | 1/4, 1/2, 3/4 |
| 2 | + halves | 1/4″ | 1/4, 1/2, 3/4 |
| 3 | + quarters | 1/8″ | every 1/8 |
| 4 | + eighths | 1/8″ | every 1/8 |
| 5 | same as 4 | 1/8″ | none |
| 6 | same as 4 | 1/16″ | none |
| 7 | + sixteenths | 1/16″ | none |
| 8 | + thirty-seconds | 1/32″ | none |
- Inch numbers (1–5) always appear, like on a real ruler.
- Lengths range from 1/8″ to 5 31/32″ and are always shown in lowest terms (1 1/2″, never 1 4/8″).
- Within a tier, the newest fraction size comes up most often, and each older size comes up half as often as the one after it. The same length is never asked twice in a row.
An incorrect answer scores 0. A correct answer scores:
points = (tier base + fraction bonus) × speed
-
Tier base reflects how hard the ruler is: 25 at Tier 1, plus 25 for each tier above that (Tier 8 = 200).
-
Fraction bonus reflects how hard the target is:
Target whole inch 1/2 1/4 1/8 1/16 1/32 Bonus 0 0 +10 +20 +35 +50 -
Speed: each tier has a par time. Finer rulers take longer to read, so par grows with the tier. Answering at or under par earns full points. Slower answers earn par ÷ time (twice par earns half), never less than 25%.
Tier 1 2 3 4 5 6 7 8 Par 3s 3.5s 4s 5s 5.5s 6.5s 7s 8s
For example, at Tier 8, 5 17/32″ answered in 8 seconds earns 250, and in 16 seconds earns 125. 3″ in 8 seconds earns 200. The game shows each tier's par next to the tier number.
These values can be tuned. If the formula changes, every past answer is re-scored with the new one, so charts and averages stay comparable.
Tier moves are based on the student's last 20 answers in their current tier. Answers from before they reached the tier don't count, and nothing happens until they've given 20 answers there.
Each answer is also measured as a percent of the points it could have earned. For example, a correct answer at twice par earns 50%, and a wrong answer earns 0%. That way a lucky run of high-bonus targets doesn't move anyone.
- Move up when at least 90% of those answers are correct and they average at least 60% of possible points.
- Move down when they average below 30% of possible points. A run of misses causes this, and so do answers that are consistently far slower than par (about 3.5× par or slower).
A student's tier is the same across all their classes, like KenKen rank. Below the ruler, a Tier Progress bar (styled like the KenKen rank bar) lists the three move-up conditions with the student's current numbers, e.g. "Answers 13/20 · Correct 92% / 90% · Points 62% / 60%". Each one gets a check mark once it's met. The bar fills to whichever condition is furthest from being met, so it reaches 100% at the moment the student moves up. Hover over it to see the move-down rule.
Play Locally (no sign-in) lets anyone pick a practice tier. Nothing is saved.
Check Ruler Game under Assignment Requirements on the class page and set Ruler Game Correct / Day. One correct answer counts as one toward the daily requirement, however long it took. See Daily Practice & Assignments.
Ruler Game charts appear below the existing charts:
| Where | Charts |
|---|---|
| All Data tab and a class's page | score over time, accuracy by fraction size (whole inch through 1/32″), how many students are on each tier |
| Student Lookup | score over time, accuracy by fraction size, highest tier played each day |
| Student My Progress | score over time, accuracy by fraction size, highest tier played each day (plus their current tier) |
The rules live in one file, js/measurement-core.js, which both the game page and the server
load. It holds the tier table, target selection, snapping, the score formula and the
tier-movement thresholds. Tuning values are in CONFIG. If you change the score formula, bump
CONFIG.SCORE_VERSION so older rows get re-scored at startup.
See Database Schema and API Reference for storage and endpoints.