# Style Guide civil-span excerpt

Original SHA256: 2e7993eac77ec119b27bfc9ace67e3d196d21d358a64c536a1dc8f60729e1abb

Examples:

- `4106 − 1406 = 2700`;
- `3486 − 1886 = 1600`.

### 5.2 Cross-axis spans

When the span crosses the BC/AD axis, use the repository-standard formula:

```markdown
BC + AD − 1
```

Example:

```markdown
4166 + 4115 − 1 = 8280
```

### 5.3 Do not mix operators

Do not apply same-side subtraction to cross-axis spans. Do not apply `BC + AD − 1` to same-side spans.

### 5.4 Civil-year note

The repository uses civil BC/AD reckoning with no year 0. This is why cross-axis spans use `BC + AD − 1`.

### 5.5 Audit categories for arithmetic

Every Arithmetic-layer check (within the Unified Revision Pass, or as a standalone Arithmetic Pass under the High-risk split) should cover at least these categories:

| Arithmetic type | Rule |
|---|---|
| Same-side BC span | subtraction |
| Same-side AD span | subtraction |
| Cross-axis BC/AD span | `BC + AD − 1` |
| Key of 23, Priestly | `25/23` |
| Key of 23, Prophetic | `70/69` |
| Key of 23, Enochian | `300/299` |