# C869 — Recover the whole49/70 common coarsening

## Question

How do the two measurements divide one primary5390-year display?

## Inputs

```json
{
  "span": 5390,
  "units": [
    49,
    70
  ]
}
```

## Sources

```json
[
  "File54 §§8.6,13.2",
  "C860"
]
```

## Opened utc

2026-09-28T02:45:07.563470+00:00

## Results

```json
{
  "unit": 490,
  "boundaries": {
    "path": "model/NT_49_70_coarsening.json",
    "sha256": "0f8f6b632e788373b74ddac612833439ab7771d12b0a72baef53e4076e4974ee",
    "bytes": 959
  },
  "partition_common_blocks": [
    3,
    5,
    3
  ],
  "partition_70_slots": [
    21,
    35,
    21
  ],
  "partition_49_units": [
    30,
    50,
    30
  ]
}
```

## Finding

70k=49j holds exactly at k7m,j10m. The whole primary span has12 common boundaries in490-year steps; the source1470|2450|1470 partition becomes3|5|3 blocks in either measurement. The extended49-grid is a comparison construction.

## Reassessment

Test reflection on the complete common grid and its source-marked partition.

## Checks

```json
{
  "whole_span": true,
  "literal_field": true,
  "partition": true
}
```

## Closed utc

2026-09-28T02:45:07.565774+00:00

## Record provenance

Exact record hash: `efff108af7686541b55686e404c8464619509f11f66b6e1b153a64d1cc9470be`

Source journal: `Research_Cycles/C0832_C0931/journal.json`