# Decision Record ## Decisions - Use a Franklin-style horizontal spindle with nested graduated glass bowls. - Treat the instrument as a friction idiophone played by wetted fingers at the rims. - Uplift the packet to V5 L2 because the subsystem plan, BOM, candidate cut-list, and promotion gates now identify where future measurements belong. - Keep all build-critical claims pending because no measured bowl set, spindle layout, drive prototype, or tuning evidence exists. - Record every artifact as `concept_only` or `pending_measurement`. - Do not create CAD, DXF, renders, pitch tables, dimensions, or drive ratios in this pass. ## Open Questions - What real bowl set, supplier, or custom glass process will define the first measured geometry? - How will the spindle interface support each bowl without point loading the glass? - What bearing and guard layout isolates water from rotating hardware? - What treadle/flywheel arrangement gives smooth motion without audible mechanical noise? - How much clearance is needed between nested bowls under rotation and player touch? - What validation fixture can measure free-bowl response before mounting and mounted response after assembly? - What minimum service clearance is needed to remove, clean, or replace one bowl without disturbing the rest of the stack? - Which guard elements can be tested on the drive rig before real glass is installed? ## Promotion Gates - L2 records subsystem intent and pending-measurement gates only; it does not authorize fabrication. - L3 requires reviewed fabrication authority and prototype validation. - L4 requires empirical build data, measured sound response, and documented revisions.