Scope: Game Timers — handheld/tabletop devices used to pace turns or rounds in games (sand timers, wind-up dial timers, digital single countdown/buzzer timers, and dual digital/analog game clocks used for chess, Scrabble, Go, etc.), including game-marketed kitchen-timer-style devices; excludes video game consoles and dedicated trivia/quiz buzzer systems (sibling: portable_electronic_games).

Seed:
1. Equivalent of harvest_date: whether a clock actually supports Fischer increment / Bronstein / simple delay — a cheap "chess clock" can look identical to a tournament-legal one but be sudden-death-only, which is invisible on most listings.
2. Watchmaker persona notices first: button travel/feel (speed of press matters in blitz, same-hand-press is a FIDE rule) and whether the two sides stay in sync over a multi-hour game — not price or color.

Sources:
[wikipedia_game_clock] https://en.wikipedia.org/wiki/Game_clock — product_type, time_control_modes_supported, flag_fall_indicator, move_counter, settability, clock_accuracy_sync, button_ergonomics — fetched, contains "Fischer clock", "Bronstein delay", "did not count the number of moves", analog flag description
[wikipedia_hourglass] https://en.wikipedia.org/wiki/Hourglass — product_type, housing_material, round_length context — fetched, contains "Sand timers are sometimes included with tabletop games such as Pictionary and Boggle"
[wikipedia_kitchen_timer] https://en.wikipedia.org/wiki/Kitchen_timer — duration_mechanism, display_type, power_source — fetched, contains mechanical/digital/hourglass technology progression
[fide_laws_of_chess] https://handbook.fide.com/chapter/E012023 — flag_fall_indicator, time_control_modes_supported, round_length (blitz def.) — fetched, contains Article 6 "The Chessclock" verbatim, Article B.1 blitz definition
[wikipedia_time_control] https://en.wikipedia.org/wiki/Time_control (redirected from Byoyomi) — round_length, vocabulary (byoyomi, blitz/rapid/classical) — fetched, contains FIDE classical/rapid/blitz thresholds
[wikipedia_pictionary] https://en.wikipedia.org/wiki/Pictionary — round_length (1-min bucket) — fetched, "A one-minute timer, usually a sand timer"
[wikipedia_boggle] https://en.wikipedia.org/wiki/Boggle — round_length (1-3 min bucket) — fetched, "a three-minute sand timer is started"
[wikipedia_catch_phrase] https://en.wikipedia.org/wiki/Catch_Phrase_(game) — alert_type (random buzzer) — fetched, "beeps at an increasing rate before randomly buzzing"
[wikipedia_toy_safety] https://en.wikipedia.org/wiki/Toy_safety — toy_safety_standard, housing_material (hazard rationale) — fetched, "ASTM F963-11", "CE Mark", "choking hazard for children under three"

Branches: product_type forks the facet set (sand_timer gets housing_material; digital_dual_game_clock gets time_control_modes_supported + button_ergonomics) per Game_clock wiki's description of how mechanism determines capability. use_context forks tournament-only facets (time_control_modes_supported, move_counter, flag_fall_indicator, clock_accuracy_sync) per FIDE Article 6's handling/default-time rules, which only bind in arbitered play.

Noise: WebSearch was exhausted this session; retail/brand spec pages (DGT, chessusa.com, Time Timer, Learning Resources, hand2mind, School Specialty, Amazon) all returned 403/404/000 on curl — no brand spec sheets secured. Relied instead on the FIDE standard, 2 game-specific Wikipedia pages used as de facto spec rows (Pictionary, Boggle), and the Catch Phrase, Hourglass, Kitchen timer and Game clock primers. Rows not turned into facets: device brand/model name (not a facet per rules), bell volume in dB (no source found), exact sand-grain size (manufacturing detail, not buyer-relevant), warranty length (not expertise).

Corrections: fixed 2 reference `kind` enum values (standard -> standards_body / regulator) and shortened 2 cold_start_questions from 13 to 12 words per validator output. Build then passed (17 facets, 2 splits, 9 references).

Corrections (2026-10-26):
- Added `product_type` value `mechanical_dual_game_clock` (dual analog/mechanical clock, two separately wound movements) with its own product_type branch; sourced to wikipedia_game_clock's "Analog game clocks" section plus a new reference, fide_mechanical_chess_clocks (FIDE Handbook C.02, Section 4 "Mechanical Chess Clocks", fetched and grepped), confirming FIDE regulates it as a distinct, currently-live equipment category — stronger than the retail listing the checker cited, which was unreachable this run (Walmart returned a bot-check page on curl and WebFetch, consistent with notes.md's existing Noise entry).
- Added a branch for `use_context = educational_classroom` (previously unbranched) and widened its `cold_start_question`/split question from 2 to 3 options so the value is actually offered.
- Added `clock_accuracy_sync` to `makes_irrelevant` in the `sand_timer`, `mechanical_dial_timer`, and `digital_single_timer` product_type branches, closing the leak where it stayed askable for single-timer products despite being defined only for dual clocks.
- Added `button_ergonomics` to `digital_single_timer`'s `makes_irrelevant`, matching the suppression already present on the sand_timer and mechanical_dial_timer branches.
- Relabelled `flag_fall_indicator.source` from `listing` to `researched`, matching its own backfill_note (photo-read for analog, flat default for digital — neither is stated listing text).
- Added "(EN 71)" to `toy_safety_standard`'s definition and to the "CE mark / EU Toy Safety Directive" vocabulary entry, sourced to a new reference wikipedia_en_71 (fetched and grepped, confirms EN 71 is the EU's harmonised toy-safety standard) alongside the existing wikipedia_toy_safety reference, which already names it inline.
- Named USCF alongside FIDE in `use_context`'s definition, listing_field_hint, backfill_note, and skip_if_known, sourced to a new reference wikipedia_uscf (fetched and grepped: "USCF is the US governing body for chess competition... represents the US in FIDE").
- Rejected nothing from the Required fixes list — all 7 applied as targeted edits; build passes (17 facets, 2 splits, 12 references).