AP Chemistry — course duration review
All nine units are built and their element counts reconcile to the item. This page turns those counts into student hours, with the constants accepted for AP Biology. The question it answers: how long is the course as built, and what would the standing cut rules save if James ever applied them? · 14 October 2026
The built course asks a student for about 108 hours, once through.
At 2 hours a day, that is 54 study days — about 11 school weeks.
The College Board plans ~140 instructional hours for AP Chemistry. The build sits 32 hours under that line.
AP Biology, priced with the same constants, came out at 277 hours. This course is 108.
Under the standing vault cut rules the course would run 70 to 80 hours (35 to 40 study days). That band is a scenario only — no cuts have been made.
Half the time is in-lesson checks: 53 of the 108 hours. Reading the lessons themselves costs 23 hours.
Where the hours sit, unit by unit
Hours on the axis, once through. The reference line is the College Board's ~140 instructional hours, spread over the nine units (15.6 h per unit).
As built vs the lean scenario
The lean band is a scenario under the standing cut rules — NOT applied; no cuts have been made. Solid = lower bound (2 checks kept per atom); pale top = upper bound (3 per atom). Gates go to an item bank, each unit keeps one 12+1-item topic test, and free response stays only on assessment pages.
Outside the once-through path
- Reveal steps: +2.5 h if a student opens every optional reveal (29,679 words: 25,092 in lessons, 4,587 in gates). They sit behind a tap, so they are not in the bars.
- Video: only Unit 2 has any — 29.6 minutes, measured from the rendered files. Units 3 to 9 have no video slots in the build. A full video track would add time this model cannot yet estimate.
- Unit 2's 14 activation questions (1,715 words) are specified but not rendered today. Excluded; they join the model only if the activation route ships.
- Unit 2 has no practice pages. Its test + practice band is the test alone. That is a content gap, not a counting one.
The judgment calls inside the numbers
The call: in-lesson MCQs are timed at 40 s, not AP Biology's 20 s quiz rate.
- AP Biology's 20 s rate applies only to its quiz parts.
- This course's schema has no quiz parts: every check sits inside a teaching-part block, and the accepted teaching-block rate there is 40 s.
What changes: lesson checks price at 53 h; at 20 s the total would read about 19 h lower, and wrongly.
The call: gate items are timed at test rates (60 s for MCQ and numeric alike).
- A gate is a cold checkpoint: the student answers away from the teaching block that coined the idea.
- Cold conditions are test conditions, so the test rate applies.
What changes: the 403 gate items cost 6.7 h of the 108.
The call: FRQs are timed per part, never per point, with part counts read from the counts file.
- Points are rubric marks; parts are things the student does. Test FRQs carry 93 parts but 116 points; in-lesson FRQs carry 33 parts but 75 points.
- Pricing points instead of parts would overstate FRQ time by about a quarter.
What changes: test and practice FRQs price at 3 min a part; in-lesson FRQs and draw tasks at 2 min a part.
The call: each of the 738 worked-example steps is timed at 60 s, on top of the prose read.
- The accepted AP Biology method treats each step as a numeric row the student works before the reveal.
- The step text also sits in teaching prose at 200 wpm; both are kept so the method matches AP Biology's verbatim.
What changes: worked examples cost 12.3 h.
The call: feedback, why-lines and reveal steps are not read on the once-through path.
- Feedback reading is already inside the per-item rates; counting its 297k words again would double-count every answer.
- A reveal is optional scaffolding behind a tap, so it is a footnote (+2.5 h), not a bar.
What changes: nothing in the bars; the footnote band above carries the reveal figure.
The call: the lean scenario is a range, 70 to 80 hours, because definition atoms are not marked in the registers.
- The cut rules keep 3 checks on a definition-quiz atom and 2 elsewhere (lessons are one-atom, so the cap is applied per lesson).
- The nine registers do not mark coining rows consistently (U1 marks none, U8 marks 17), so the honest band runs from every atom at 2 to every atom at 3.
- The true figure sits nearer the lower end: definition atoms are a minority.
What changes: nothing. The scenario is shown so a cut decision, if one is ever wanted, starts from numbers.
The detail, collapsed
Per-unit hours table (the numbers behind both charts)
| Unit | Prose | Lesson checks | Worked examples | Gates | Test + practice | Video | As built | Lean low | Lean high |
|---|
Components are shown to two decimal places; totals are computed before rounding. The two cross-checks agree exactly: summing the six components across units and summing the nine unit totals both give 108.33 h.
Constants used (AP Biology's corrected constants, accepted by James 14 Oct)
| Element | Rate |
|---|---|
| Teaching prose (ideas, outcomes, notes, worked-example text, captions) | 200 wpm |
| In-lesson MCQ | 40 s |
| In-lesson numeric item | 60 s |
| In-lesson draw task | 2 min (the FRQ-part rate) |
| In-lesson FRQ | 2 min per part (33 parts) |
| Worked-example step | 60 s (738 steps) |
| Gate item (MCQ or numeric) | 60 s (test rates) |
| Test or practice MCQ / numeric | 60 s |
| Test or practice FRQ | 3 min per part |
| Video | measured file durations (U2: 29.6 min) |
| Feedback, why-lines, alt text | excluded — inside the item rates / screen-reader only |
| Reveal steps | excluded from the main path; footnote at 200 wpm |
Gary's slower-rate variant of these constants was rejected; the accepted AP Biology set is used verbatim.
Method and reconciliation
Counts come from element_counts.json in this folder, which walks every unit the way its own builder does and reconciles exactly with the rendered pages' clickthrough reports — see COUNTS_NOTES.md. The arithmetic, every constant and every judgment are recorded in DURATION_MODEL.md beside this page. The lean scenario applies the standing vault cut rules: checks capped by atom (2, or 3 on definition atoms), gates moved to an item bank, one 12+1-item topic test per unit (12 MCQ plus one FRQ at the unit's average test-FRQ length), free response kept only on assessment pages. Practice pages, prose, worked examples and video are untouched by the scenario.