# Use and verify fixings (/guides/verify-fixings)

A **fixing** is an index level taken at a scheduled time and published as an official value. Fixings are recorded in
an append-only ledger where each entry is hash-linked to the one before. A fixing can't be changed without the
change showing up.

## Latest fixings [#latest-fixings]

```bash
curl https://data.tryopengrid.com/v1/fixings -H "Authorization: Bearer $OPENGRID_API_KEY"
```

`data.indices` holds each settlement index with its latest hourly and daily fixings, and any provisional value still
waiting to be finalised. `data.ledger_head` is the newest ledger entry.

<Callout type="warn" title="Decimal strings">
  Fixing values are strings such as `"2.2494934019"`. Parse them with a decimal type (`decimal.Decimal`,
  `BigDecimal`), never a float, so no rounding creeps in before settlement.
</Callout>

## One index's fixings [#one-indexs-fixings]

```bash
curl "https://data.tryopengrid.com/v1/indices/h100-80gb-sxm5/fixings" -H "Authorization: Bearer $OPENGRID_API_KEY"
```

## Verify a fixing [#verify-a-fixing]

`GET /v1/fixings/{fixing}/verify` recomputes the fixing from its stored inputs and checks its hashes and its links
to its neighbours. `GET /v1/fixings/chain/verify` checks the whole ledger:

```json
{ "ok": true, "checked": 18240, "break_count": 0, "breaks": [], "head_seq": 18240, "head_hash": "9c1e..." }
```

Store `head_hash` alongside the fixings you settle on. If you call `chain/verify` later and it still passes with the
same history, nothing you relied on was altered.

## Corrections [#corrections]

A wrong fixing is never edited. It is **restated**: a new ledger entry carries the corrected value and the reason,
and the original stays. `GET /v1/fixings/restatements` lists every restatement.

## Methodology [#methodology]

`GET /v1/fixings/methodology` gives the schedule, thresholds and correction rules as data. The full method of every
index is in `GET /v1/methodology/indices`.