| Model era table (tube lines and the solid-state lines) | 1965-2002 | 14 | Era dating: this is the primary instrument for Sunn because the serial number carries no date information. |
| Build history milestones (who owned Sunn) | 1963-2002 | 5 | Needed to interpret model names that were reused (Model T 1968-75 vs 1998-2001). |
| EIA component codes (transformers, pots, speakers) | 1965-1980 | 0 | Component codes date the PART, not the amp: a replaced transformer/speaker/pot can be newer than the amp. Upper-bound rule — the amp is not older than |