# UTFANSWF v21 — Row 20 SN Geometry Probe

**Context:** DIAGNOSTIC_NON_GATING. No physics, thresholds, datasets, parameters, or gate verdicts changed.

## SN nodes

| Slice | z | data | theory | residual | pull sigma | chi2 |
|---|---:|---:|---:|---:|---:|---:|
| SN mu z=0.10 | 0.100 | 42.000000 | 39.707042 | 0.177029 | 0.885146 | 0.783483 |
| SN mu z=0.35 | 0.350 | 43.100000 | 41.573176 | -0.589104 | -2.634554 | 8.445196 |
| SN mu z=0.70 | 0.700 | 44.200000 | 41.749589 | 0.334483 | 1.365521 | 1.864647 |

## Midpoint geometry

| Quantity | Value |
|---|---:|
| midpoint slice | SN mu z=0.35 |
| linear interpolated midpoint residual | 0.242635 |
| actual midpoint residual | -0.589104 |
| midpoint curvature residual | -0.831739 |
| linear interpolated midpoint pull | 1.085302 |
| actual midpoint pull | -2.634554 |
| midpoint pull curvature | -3.719856 |

## Interpretation

- SN geometry probe tests whether the z=0.35 node is a simple offset or a midpoint curvature/pivot residual.
- The z=0.35 residual is not explained by a simple linear offset between low-z and high-z SN nodes.
- The midpoint node is the dominant SN stress contributor.

## Verdict

SN_midpoint_geometry_probe_complete; diagnostic only; no physics, thresholds, datasets, parameters, or gate verdicts changed.
